Just as a note, the absolute sovereignity model, if compared to nation-states, would be a confederation, not a federation.
A primate who presides with real, but limitted power, over autocephalous churches, would be a federation.
And then, we have the RC which would be, in that analogy, a unitarian state without autonomous unities.
My understanding is that the traditional model, the one inspired by the Holy Spirit is the second one.
The thing which mitigates against this understanding is that in the first one thousand year history of the Church there is no mention of such a person presiding over the autocephalous Churches. There is no mention in any of the ecumenical councils and nor is there even a single canon about a universal primate and his presidency, his powers, his obligations, his limitations. If he existed he was quite invisible to the eye and unnoticed by the bishops.
This power was divided between two people: the emperor in Constantinople and the pope in Rome. Again making use of the political metaphor, the emperor war more like a chief of government and the pope was the chief of state. Indeed, it seems to me that the role of the primate was very much like that of the current role of the queen of England. It *is* symbolic in many ways but not completely devoid of certain responsibilities.
My current impression is that things happened thus: each diocese was indeed autonomous. They gathered in regional assemblies which required the "presidency" of one of them. Because those were not democratic times, but very hierarchical ones, the natural choice was the bishop of the most powerful and/or traditional city of the region. That is the same structure we see inside the lower orders: deacons and a protodeacon, presbyters and a protopresbyter, bishops and a first bishop, the archbishop. It's natural that in a gathering where all the laity and clergy were represented, one of archbishops should be a "first among equals".
Now, this honour was first given to Rome for three main reasons: it was well known for the Orthodoxy of its faith in face of heresies elsewhere, it was the city of martyrdom of Ss. Peter and Paul and it had been not only the capital, but the very cradle of the empire. Even RC theologians will acknowledge that the current hyperspecification on a special inheritable charisma of St. Peter is a "development" of dogma from the initial claims that were clearly about the honour of being the place of martyrdom of the two most well known and respected Apostles. I would also add a fourth reason that is never explicitly stated but I feel it is fair to imply from the texts: Rome was outside the direct influence of the emperors, that being one of the reasons imperial heresies could be resisted there by Greek popes fleeing from the hellenic side of Christianity and well aware that only being outside the empire and using the authority confered by tradition to the city they could stand up against the secular force of government. In fact, it is my opinion that much of the "all the church must be subjected to the Church of Rome" talk came from pious man who knew that this see outside the influence of politics and shallow philosophy was the only hope for Orthodoxy. It's a pitty that when confronted with the first "local" emperor, it could not resist his own heresies.
Although it was never expressed in juridical terms, the culture of the time justifies the understanding that there should be some obedience toward the "first among equals", but it is meant to be "soft power" obedience and not the strict institutional kind of obedience Rome later claimed. We can look at the Justinian code for a consolidated expression of the role of the primate. In this code Justinian calls the primate "head of the bishops" and "head of all churches". Notice the difference between these terms and that of "head of the Church" even if a "visible" counterpart of an "invisible" head.
Back to the political metaphors, I would like to call your attention to the very interesting system of Switzerland, which is, to my knowledge, one of the best forms of government in the world today. Instead of having a president as head of government, they have a Federal Council:
The Federal Council is the seven-member executive council which constitutes the federal government of Switzerland and serves as the Swiss collective head of state.
While the entire council is responsible for leading the federal administration of Switzerland, each Councillor heads one of the seven federal executive departments.
Each year, one of the seven Councillors is elected by the United Federal Assembly(Fabio's note: more or less equivalent to the Congress) as President of the Confederation. The Federal Assembly also elects a Vice President. By convention, the positions of President and Vice President rotate annually, each Councillor thus becoming Vice President and then President every seven years while in office.
According to the Swiss order of precedence, the President of the Confederation is the highest-ranking Swiss official. He or she presides over Council meetings and carries out certain representative functions that, in other countries, are the business of the Head of State. In urgent situations where a Council decision cannot be made in time, he or she is empowered to act on behalf of the whole Council. Apart from that, though, he or she is a primus inter pares, having no power above and beyond the other six Councillors.
The President is not the Swiss head of state (this function is carried out by the Council in corpore, that is, in its entirety). However, it has recently become usual that the President acts and is recognized as head of state while conducting official visits abroad, as the Council (also by convention) does not leave the country in corpore. More often, though, official visits abroad are carried out by the head of the Federal Department of Foreign Affairs. Visiting heads of state are received by the Federal Council in corpore.
The head of state is the collegiate and the "president" is not president of the country, but president of the collegiate. This is a huge difference. This seems to be exactly what Justinian was saying when calling the pope "head of the bishops".
In fact, the church, in the world, is governed by the bishops, among whom, one who presides over *the collegiate*, not over the whole Church. This governance of the whole Church belong to the Holy Spirit exclusively. There is no such a thing as an invisible and a visible head *of the Church*. The Church has just one *visible* head: Our Lord Jesus Christ. In the world, it is governed by the bishops who, ad hoc, assemble to take decisions regarding their regions, and, on ocasion, assemble from everywhere of the Christian world, under the "presidency" of the primate, even if through his legates, an incovenience due to distances in the first millenium, but easily solved today. These gatherings, though, are not called by the "president" of the collegiate, the "head" of the "head of state", but by the "head of government", in that case, the emperor. Today, thanks God, there is no universal emperor. It means that a new "head of government" would have to be found for the collegiate and I think this honour should be given to the collegiate itself.
Should this system be fully reimplanted with the necessary adaptions for the current days, the Orthodox jurisdictions would have to compromise by fighting ethnophyletism with all their forces to allow the universalismo of the Church to shine unhindred. Rome would have to give up its monarchical pretensions and their correlate errors like infallibility. It wouldn't have to give up it's philosophical traditions but would have to bring it back to ground in relation to practical ascesis, the same relating to the excesses relating to the Theotokos and the recovery of the Western Orthodox phleroma, the roots of which can still be found in some of the most traditional monastic orders that still exist in RC. It certainly would not mean the byzantinization of RC but of the cultivation of the right seeds.