Which brings up the Incarnation. Which is more important, the theology of Apostolic Succession or the theology of the Incarnation? The non Chalcedonian churches do not have the theology of the Incarnation the same as the Chalacedonian churches do (which includes many Protestants).
Also, the Malabar Christians didn't have the best of luck with the Portuguese Jesuits at times. They were accused of being Nestorians, and many of their books were burned. Some have not united with the Roman Catholics to this day as a result.
Both the EOC and the RCC have signed statements with all the non-Chalcedonians over these matters which proclaim they share the same faith regarding the Incarnation, and that past misunderstandings 1300-1600 years ago are no longer relevant to the situation today. The Copts, Armenians, and Syrians are not held to be followers of Eutyches, the Assyrians are not held to be followers of Nestorius. Communicatio in sacris exists among the faithful in these Churches, even if it does not yet extend to the heirarchy.
However, this merely reinforces the point that the visible divisions in the Church are the result of disagreements among the Bishops, and not at the level of the faithful, who make up the Church through profession of the same faith, reception of the same sacraments, and obedience to their immediate legitimate pastors and heirarchs.
I can't emphasize enough that the disobedience or schism or heresy of a Bishop need not have any effect at all on his flock if they simply follow the traditions they have received from those who went before them - "ut quod apostoli docuerunt, et ipsa servavit antiquitas nos quoque custodiamus" - "what the Apostles taught and what antiquity itself observed, let us also endeavour to keep" - in other words: "following the saintly fathers".
Also, the Malabar Christians didn't have the best of luck with the Portuguese Jesuits at times. They were accused of being Nestorians, and many of their books were burned. Some have not united with the Roman Catholics to this day as a result.
Rather, because of Portuguese missteps and heavyhandedness, some Malabar Christians broke off with the RCC and have not returned. The vast majority though, are in the RCC despite these problems. The Portuguese allowed colonialism and Euro/Roman-liturgical/theological-centrism to stand in the way of communion. They also caused the same problems in Ethiopia. This says more about the Colonial era Portuguese then it does about the Ethiopians or Malabarese.