The history was more complex. There are Syrian Christians (600AD), Catholics (1500), Anglican Protestants (1800) and more recently, evangelical Christians. Each group is linguistically and culturally distinct. https://en.wikipedia.org/wiki/Christianity_in_India

Mangalorean Catholics for instance are mostly Saraswat Brahmins who converted around 1700s https://en.wikipedia.org/wiki/Mangalorean_Catholics