Well, I was thinking of just the division on this issue, which is a pretty big one, but I see your point. Of course, the other side would probably look at the same history and say that the “real” church never changed, they just had a never-ending series of heretics splitting off from them. If you take that perspective, then I guess you never have to worry much about Christian unity at all. Anytime there is an argument, you can just arbitrarily make a line, then say everyone on the other side of it is suddenly not a Christian anymore. Problem solved!
Exactly. To a very considerable extent, that is exactly what happened. The winners decided what doctrine was orthodox and what was heretical.