To the best of my knowledge, there has only been a period of three years in which we had "pure" theology.
Even as early as AD 50, there was division.
In 1 Cor. 3:4-6 we read:
"4 For while one saith, I am of Paul; and another, I am of Apollos; are ye not carnal?
5 Who then is Paul, and who is Apollos, but ministers by whom ye believed, even as the Lord gave to every man?
6 I have planted, Apollos watered; but God gave the increase."
Even in the second century it can be argued that:
So far as we can tell, all of these groups appealed to written authorities for their views, texts that were allegedly penned by apostles.
Some groups subscribed to Gospel accounts written in the names of Thomas or Philip or Peter, or attributed to Matthew or John or
Mark. We know of Christians in the TransJordan who adopted a Hebrew Gospel similar to our own Gospel according to Matthew,
of Christians in Egypt who used the Gospel of the Egyptians, of others there who accepted the Gospel of the Hebrews, of yet others
who subscribed to the Gospel according to Thomas; there were Christians in Rhossus who revered the Gospel of Peter, Christians
in Rome who read a synopsis of Matthew, Mark, and Luke, Christians in Syria who read an expanded version of this that included John,
Christians in Alexandria who read only John, and Christians in Asia Minor who read only Luke, and that in a somewhat truncated form.
Studies in the Textual Criticism of the New Testament, Bart Erhman and James Grey, Edited by: Bruce Metzger, Brill, Linden, Boston, Copyright 2006, Chapter II, The Text of the Gospels at the end of the Second Century, Introduction, Diversity in Second-Century Christianity, p. 72
So technically, from about AD 33 until now, there has been no "pure" theology. There has always been some influence. Whether it was early in that some Christians claim to follow only the teachings of one Apostle or another, or one theolgian or another.
So each and every age technically, has been "contaminated" or "corrupted" in one form or another.
Some say Calvinism "contaminated" or "corrupted" Christians, personally, I believe Arminianism did the same.
God Bless
Till all are one.