Greetings in that Divine and Most Precious Name of Our Lord and Savior Jesus Christ!
On topic: the LXX and the MT should be used together, there shouldn't be a LXX-only movement or something.
Why? The OT of the Church is the LXX, so personally I see no reason to use the MT. I can see some reasons for comparing the two from time to time, but the LXX is the Christian OT, not the MT.
I agree, while there are some wonderful insights in the Masoretic texts, in truth, there are also blatant revisions to argue or apologize for post-Christian interpretations of Old Testament verses. I have read the modern JPS translations of the Tanahk and they are blatantly ideological at times and in almost polar opposite of several fundamental Christian uses of the Old Testament. For my part, I prefer the Septuagint, and often I am skeptical of the KJV because it uses the Masoretic texts to proof-read against the Septuagint versions, largely because the English decided that they liked Jewish folks more than Roman Catholic folks, which is bitterly ironic and any Jewish person considering the history of Western Europe and even England might just have a cynical laugh.
We should consult the Masoretic texts from time to time for comparison of Scriptural evolution, but we should only examine such translations as literature, not Sacred Scriptures. Only those versions which have been adopted by the Holy, Catholic, Apostolic Church are legitimate today, and these include the Septuagint and the Vulgate.
Its interesting to note that the Ethiopian Jews still use the Septuagint, Why?.
Because that's what the diaspora Jews of the first few centuries had. Ethiopia is relatively isolated, so it makes sense.
There are some scholars, even Ethiopians, who assert that the Ethiopian Jews weren't initially Jewish at all, but rather are an extreme reaction to some of the Fundamentalists who were sparked into rivalry during the Sabbatarian divisions oriented around Abba Stephen. Several sects pushed for Old Testament revivals such as practicing elements of the Law, and also Saturday Sabbath. Some folks have argued that some of these sects went so far as to revert to Judaism, sort of like the modern pseudo-Christian sects like the Hebrew Israelites and other Old Testament oriented Christian heresies. I'm not sure, there is indeed some merit to this argument, however I would say that perhaps what is the truth is that there was a small group of indigenous Jewish groups who were revived by new-comers from the Sabbatarian movements. Either way, the Ethiopian Jews by virtue of geographic and political isolation were entirely separated from the Jewish groups of the Orient and essentially received all of their Jewish stuff from the Church, including the Bible and many aspects of their worship services which are strikingly similar to those of the Tewahedo Tradition (hence why some scholars have asserted that they were actually Christian revisionists and not initially Jews at all). I think the truth is somewhere in the middle.. Realistically after centuries of economic and socio-cultural persecution, by the modern era the Ethiopian Jews were hardly even Jewish anymore by most standards of Judaism, they were actually a lot like some of these pseudo-Christian-Jewish contemporary interpretations.
I believe there were indeed indigenous Jews in Ethiopia before the Solomonic Restoration, however I think they declined almost to the point of non-existence and were only revived by an influx of Christians and other "converts" during the Sabbatarian controversies of the mid-15th century.