You summarize well the UGCC revisionism, shared by some/many supporters of Ukrainian autocephaly over canonicity. There are real facts in that, just as a counterfeit bill has to look like the real thing to work.
I'll just interject where the story is diverted and bent (not by you personally, but by the narrative supported by the mythology of Halecki and Bp. Gudziak, and like minded Ukrainian phyletists):
It is more historical than theological, particularly among those who are of the UGCC and perhaps to some extent of the Byzantine Catholic Church (from the Eparchy of Mukachevo). Both of those churches were part of the Church of Kyivan Rus', which was always subject to Constantinople until its fall.
Constantinople fell in 1454, but the Metropolitan of Kiev and All Rus', Met. St. Jonah, was consecrated autocephalously in 1448. The Metropolitanate had been autonomous at least since 1354-89 (it took a couple of Tomes), partly in response to the attempt of the Grand Duke of Lithuania using its possession of the remains of Kiev itself in promoting a separate metropolitanate from the Metropolitan of Kiev, then resident in Moscow. At the same time the see was translated from Kiev to Vladimir-on-the-Klyazma, and the choice of Metropolitan vested in the Grand Duchy of Moscow.
Then, of course, Moscow gained autocephaly. But the areas where the UGCC / BCC come from (western and south-western Ukraine) were outside the territory of the Tsardom at the time of Moscow's autocephaly.
The Tomes issued by Constantinople around 1354 and finally confirmed in 1389 subjected all dioceses outside of the Grand Duchy (it was not a Tsardom until almost a century after Moscow's autocephaly) of Moscow to the Metropolitan of Kiev resident there.
They were under Polish rule.
In 1451 King Casimir of Poland issued a diploma recognizing Met. St. Jonah's authority over his suffragans in Lithunia, including Kiev-he only refused to let the bishops of Halych and Peremyshl' (where his predecessors, under express instructions of their supreme pontiff, had driven out the Orthodox bishops and installed the Vatican's Latin bishops) recognize the Metropolitan's authority-ironically, or perhaps apropos, their successors would be the bishops who refused to sign the "Union of Brest" and who formed the core in which the Ukrainian Orthodox Church continued. The diploma explicitly recognized his right to the Metropolitan's residence and Cathedral in Kiev and in Vilnius (where the future Metropolitans of the "Union of Brest" actually resided).
I think that probably because of a combination of Polish reluctance to have the Patriarch of Moscow's influence on its territory and the realization of the Ruthenians in Poland that they were different from the Ruthenians under the Tsar (by this time, the languages were well on their way to splitting), Constantinople appointed a replacement Metropolitan of Kyiv under its own jurisdiction.
The deposed EP and then Latin "Patriarch of Constantinople" in Old Rome, Gregory Mammas, at the direction of the deposed Metropolitan of Kiev, Isidore the Apostate, also in Old Rome, ordained Gregory Bolgarian/the Bulgarian as Metropolitan of Kiev and Lower/Little Russia (Russia Inferior). Moscow and Upper/Greater Russia (Russia Superior) was supposed to stay under Isidore's jurisdiction, although he had been deposed by its Holy Synod in 1441. King Casimir then, on instructions from his supreme pontiffs (Calixtus and Pius) and "Pat." Gregory and "Met." Isidore, withdrew his recognition of Met. Jonah and forced the bishops under his control to do the same. The bishop of Briansk, Chernihiv and Smolensk, in Lithuanian territory at the time, refused and fled to Moscow. Many Lithuanian nobles did the same (e.g. the family of Bishop Alexander Galitzin of Toledo and the Bulgarian Diocese of the OCA and his Academy Award Oscar winning uncle Alexander Golitzen). Half a century latter Moscow would set the precedent of gathering Briansk, Chernihiv and Smolensk into Muscovy.
Met. St. Jonah sent an encyclical, confirmed by a Holy Synod of the Metropolitinate, to the bishops in the territory of the King of Poland, the Grand Duke of Lithuania and their Orthodox nobles, denouncing Gregory, Florence and Constantinople's involvement in both. When Met. St. Jonah fell asleep in 1461, his successor had the bishops swear on the relics of Met. St. Peter the Galician to pledge their allegiance to him, and to denounce "Gregory, excommunicated from the Catholic Church, who calls himself 'Metropolitan of Kiev'." For his part, Met. Gregory, after the death of his mentor Isidore, went on to try to be accepted in Moscow, having first, in 1470, renounced those who ordained him and confessed to the EP in Constantinople. EP Dionysius I, trying to reassert jurisdiction over Kiev and All Rus', acknowledged him with the instructions to all the Rus' wherever (including Moscow) of accepting bishops only recognized by Constantinople. When Met. Gregory died in 1473, Old Rome had given up on the Union of Florence, New Rome appointed a Metropolitan Spyridon of Kiev for Moscow and Vilnius who was received and accepted by neither-instead being imprisoned a fraud. In reaction the Metropolitan of All Rus' in Moscow and his Holy Synod had all bishops swear on consecration not to receive any Metropolitans from Constantinople. Vilnius elected a successor Misael, who carried the title "Metropolitan-elect" as neither Old Rome, New Rome nor Moscow confirmed him. When he died in 1480, the situation still remained with Moscow, Constantinople and Vilnius all claiming Kiev when the Tartars sacked the city in 1481-4, sending the sacred objects among the booty to the Metropolitan in Moscow. Kiev remained a ruin until the Cossaks and the illegal (but canonical) Ukrainian Orthodox Metropolitinate of Kiev, and especially after its legalization in 1631, rebuilt it. The canonical status remained in contention until 1589-93, when Moscow released it to Constantinople in return for official and formal recognition of Moscow's autocephaly and elevation into a Patriarchate.
Then, by 1686, Russia had made its "deal" with the Hetmanate and succeeded in wresting the Metropolitanate away from Constantinople (traditional Ukrainian view).
True, but skipped over a few things.
The Orthodox opposition in UKraine, Poland and Lithuania had survived the debacle of 1596, and with the help of the Metropolitan of Moldavia and the Patriarch of Jerusalem, supported by the Cossacks in Kiev itself, had appealed to Moscow to invade and reunite the Metropolitinate to the Patriarchate, but Moscow was in no position to do so. By the time Moscow could, Met. St. Movila had consolidated the Ukrainian Orthodox Church. The Pereslav Articles, published by the Kievan Cave Monastery in 1559-the Czar's negotiator, Prince Alexei Trubetskoy, one of the many scions in the Tsardom who were then avenging their ancestors being forced to choose between conversion or Orthodoxy and who fled to Moscow, had to acknowledge the autonomy of the Kiev Metropolitinate under Constantinople, as it had been since 1589. When Russia forced Poland to sign the Treaty of Eternal Peace in 1686 (negotiated by Basil Galitzin, another one of the scions and a relative of the above mentioned Alexanders), it contained a clause making Poland promise the Orthodox their rights denied them and made Russia the guarantor of that. Poland, however, continued to persecute the Orthodox until the Eve of the Second Partition. In view of this, and a decade of a vacancy of the Metropolitinate in the Hetmanate-with almost three decades of a locum tenens in Kiev appointed from Moscow, in 1686 the Metropolitinate of Kiev was translated back to the Patriarchate of Moscow, where it has remained (but hopefully soon will no longer).
In the midst of all this, the Ruthenians in Polish lands had had enough. They wanted to preserve their rites in the Catholic-dominated land and not to become Latin Catholics. They either knew that they couldn't be placed under the Patriarch of Moscow and/or didn't want to be. So their hierarchs made the deal in 1596 (the Union of Brest) whereby the Church of Rus' in Polish lands would be placed under the Pope, but preserve all its rites. In 1646 the Union of Uzhhorod did the same thing for the Eparchy of Mukachevo, now the Byzantine Catholic Church, south of the Carpathians. Many of the people disapproved and the issue was not really resolved until almost 1700 when all the dioceses joined the Union. (Russia continued to encroach on Polish territory, and as it claimed territory that had entered the Union, it forcibly dissolved it. So Kyiv switched back to Orthodox, then Volyn, Kholm, etc.)
Ukraine isn't Polish territory. As pointed out above, it remained Orthodox, in particular Kiev which was only nominally part of the "Union," and that only for 24 years.
After Poland-Lithuania fell, Austria reinforced the union in its territory so that between 1785 and the early 1910s there was no Orthodox presence at all in its province of Galicia (Halychyna).
Actually, the Emperor Joseph, touring his new lands, was surprised by a delegation of the resident Orthodox petitioning for a diploma for a Church. The direct result is St. George Cathedral in L'viv, at present serving as the Cathedral of the Ukrainian Orthodox bishop of L'viv since his Cathedral, the old St. George, was seized by the UGCC-old St. George's bishops refusing for a century to sign the "Union." There was an increasing problem in Galicia of people returning to Orthodoxy, many not staying there going across the border to Ukraine or just to the Crown Land of Bukowina, where they eventually made the majority of the autocephalous Metropolitinate of Czernowitz. The Czar recruited most of the clergy involved in bringing the Cholm eparchy back from Galicia.
So, to put it short, these people claim that their church is the original Orthodox Church of Kyivan Rus' which fled to the Pope for protection during the Polish times, and that the Russian Metropolitanate of Kyiv was an attempt to steal it away and put it under Russian influence.
The creation of the separate Metropolitinate of Kiev, as shown above, had no Russian involvement until 1556, or really, until 1659, when it appointed the first locum tenens in Kiev.
This is why they call their leader, Major Archbishop Shevchuk, a Patriarch, even though he is not officially denominated as such. I think that many of them would be open to leaving the Union, but not if it meant that they had to be placed under the hated Russian rule. Only if they could be autocephalous or, at least, under the Patriarchate of Constantinople, which they feel was their rightful jurisdiction before the Russians stole it away from them. The Russian Empire and later the Soviet Union are blamed for destroying Ukrainian independence through the alliance with (and later absorption of) the Cossack Hetmanate in the 17th Century, the Ems Ukase in 1876, the Holodomor, etc., etc. In Western Ukraine today, which was under Austrian rule, they sell t-shirts that read, "Thank God I am not a Muscovite." If there were an independent Ukrainian Orthodox Church, many of these people would probably join it. (In fact, many did when the UAOC and the Kyivan Patriarchate arose at various times. The UAOC drew off a number of American UGCC faithful as well but the Kyivan Patriarchate not so much.) I think there is an attitude among some of those who are more nationalistic that they are "Ukrainian Orthodox in Exile" until such time as a Ukrainian national church can be properly and securely formed.
That accurately sums up their propaganda. The truth lies elsewhere, as shown above.
The BCC folks (Mukachevo Eparchy) do not consider themselves Ukrainian, so they are somewhat mixed. I don't know so much about their feelings on the matter, although some among them also resent what they feel was the forced nature of the Union of Uzhhorod in 1646. I'd be interested to hear more about that.
I've posted a bit just recently on that on another thread. Lord willing, if needed, I'll post more later.