I am a Catholic. Why should I consider becoming a Christian?
I now know more distinctions (apparently Catholicism requires duty and salvation is process, unlike Protestantism?) but I still think they're of a similar branch (Christianity) so I just wonder the social factor
Protestantism hasn't even existed for a thousand years. Heck, even the Great Schism between Eastern Orthodox and Romans Catholicism churches happened less than a thousand years ago (though that should become no longer true within our lifetimes).
Sure, but this thread isn't about infighting among Christians broadly, it's specifically about the use of "Christian" and "Catholic" in a context where they seemingly mean different things.
To be honest I find most of this thread incredibly frustrating, because so many people are explaining Christian schisms to OP, as though they don't already know about that. But that's not what they asked.