Politics Why are there a million different types of Christians?

[Spas]

Christianity's view on Isa (Peace be upon Him) is incredibly contradictory and has changed a lot over the past few millenia.

Empty assertion. The teaching of the Church is based on the teachings of the apostles and Church fathers, which are of course based on the teachings of Christ. If you're going to assert that it changed in such a drastic manner that it's "incredibly contradictory" you should elaborate on that, unless that's just empty extrapolation from the pov of islam.
Also, you simply miss the larger point. The point wasn't that "his message got corrupted therefore he's a bad prophet". Every message gets corrupted and misinterpreted by someone, the point was that his message specifically went extinct, according to you, and did so basically instantly, and in this gave birth to the largest "false" religion ever. This is an unprecedented failure and you can't disagree with that in good faith.

What about Christianity and its several prophets? Were they failed prophets just because they couldn't keep the message around for long enough?

What do you mean by this? The Christian message is still very much around.