Christianity's division will be its doom, I'm afraid. If all who professed the Christian faith, both past and present, were part of the same communion, that would be the most powerful witnessing tool imaginable, and converts would come in from all over the globe. The fact that this is not true and that these divisions remain, and that self-professed traditionalists revel in this fact, is probably the biggest contributor to the global decline of Christianity and the rise of agnosticism and the so-called "nones". (Islam is also declining since the ISIS-supporting Sunnis, non-ISIS-supporting Sunnis, and Shiites all keep killing each other. Christians don't kill each other over that kind of stuff anymore, thankfully). Anti-ecumenism might sound like being faithful to Tradition, but a century from now when there are only 10 or 20 people who share the same "tradition" as you, will that make anything better?
At least the agnostics are all more or less united in the fact that they don't profess to know anything important, and so they don't bother with preserving old divisions and hatreds in the name of being "faithful" and "traditional". They've got a leg up on religious people in that respect. And so the third millennium will probably end up belonging to agnosticism, I'm afraid. That's not what I want to see, but it seems inevitable.
Traditionalist churches, both Roman and Orthodox, that I know of are full with faithful churchgoers and their retention rates seem to be above the average, at least for a non-scientific informal assessment as mine.
The pentecostal and neo-pentecostal churches in Latin-America grow because of their firm preaching that "evangelicals" are the true church and Rome is a corruption of it.
Contrary to liberal and ecumenist mores and common-sense, it is a firm advocacy of your best understanding of non-compromising truth that attracts people, not the opposite.
People defect to ISIS and other radical groups because of the *lack* of healthy commitment to truth in their own cultures. It is relativism, liberalism and ambigous statements about eclesiology, dogma and faith that make them disbelief the seriousness of their churches and, like a starving person who ingests dirt and earth out of desperation, they cling to anything that look, even if in a corrupt way, to an honest sincere commitment to truth.
The more leftists, liberals and ecumenists succeed, the more ISIS, Putin, Golden Dawn, Anti-Jews and globalist meta-capitalists and their likes will also succeed. They are not opposing groups, but the whip and the carrot. Revolutionary left and revolutionary right are different symptoms of the same disease.