Livius, Constantinople was elevated above more ancient Churches of Alexandria and Antioch for political reasons, and even (older) Rome itself became the Holy See (rather than Antioch) for the same reason.
There is nothing in the Bible that identifies the city of Rome as the Christian "Mecca." It became that because it was the imperial capital. The proceedings from the Third and Fourth Ecumenical Councils make that very clear.
Moscow has every right to consider itself the Third Rome given that the EP is a virtual prisoner of a Muslim state, a relic of history. The MP, on the other hand, has over 80% of world's 300 million Orthodox in his fold. Even more when one adds other Slavic Orthodox Churches (Serbian, Ukrainian, etc.) which would very likely side with Moscow, politicis notwithstanding, because the laity would.
Any reunion with Orthodox without Moscow would be utterly meaningless; in fact it would be a new round of creating a new "uniate" controversy, drawing perhaps 10% of the current orthodox fold and destroying any chance of reunion for ages to come.
I am confident that any reunion will include the Orthodox Church as a whole, with all its Patriarchs and Metropolitans standing united.
As far as the West is concerned, they must show historical and synodal respect for the seniority of Constantinople, but one must be very careful not to marginalize the vast majority of the Orthodox world, especially if such marginalization is based on not much more than sheer prejudice vis a vis Moscow.
Oh, I agree. The participation of Moscow is essential, and it is true that there are understandable historic reasons for Moscow’s proclamation of itself as the “Third Rome.” I think that a lot of the historical hard feelings between the different Orthodox churches are now being resolved, by the Holy Spirit and the good will of all involved, and that the future will be quite different (and a lot better!).
Even though the Communists attempted to kill Christianity forever in the relatively short period of time they held sway, without the Russian Church, the savagery of the hundreds of years of assault on Christianity by Islam would have resulted in a far more horror filled world today...a world of islamic hell.