Christianity is not immune to that as we have real-time examples of individuals who have twisted Christianity to suit their personal tastes.
The Reverend Fred Phelps a frequent object of study on WonderCafe.ca more than WC2 certainly did not reflect a tradition so much as he claimed to.
The Reverend Creflo Dollar a recent object of study here also does not reflect a long standing tradition so much as he and others of his ilk claim to.
Both demonstrate extremely well that charisma can trump Christian doctrines and sometimes quite handily.
Like it or not we have a long chain of Christian writings even if one eliminates the scriptures themselves we have copies of Christian writings that we can trace to the first century. We can see, in those writings who and what was being referenced and we can also see how various doctrines of Christianity were shaped and formed. We can also see where the Church universal dealt with issues and we can also see where the Church couldn't tolerate the differences and ultimately split.
In all of that we see that the greatest influence on Christianity has been more of a philosophical issue than it is a source material issue.
The notion that someone, even a Constantine, could simply waltz in, tell everyone to think and radically re-engineer the Christian faith is preposterous. Especially in light of the notion that what the Church has historically deemed heretical and invested a great deal of time and energy into eradicating still finds articulation in the Church today.