St. Thomas was already busy Christianizing India while Joseph of Arimathea was Christianizing Wales in the FIRST CENTURY ~ so they had at least a thousand years to work this out before Rome sought supremacy over all the more ancient Christian congregations in the far East and far West.
I would guess the rationale here is that the Roman Catholics in Tranta see an opportunity to pick off the Christians from St. Thomas mission as they get off the Boeing.
That's what you meant, right?
I'm not sure I can use the word Christian in association with them, isn't that the whole conflict?