Historically that's not true. Christianity was often integrated with pre-existing pagan practices. In fact it was pretty common.
You do understand that Jesus and his apostles foretold the corruption of Christianity don't you?
Jesus' parable of the "wheat and the weeds" foretold that the devil would sow a crop of poisonous weeds (counterfeit Christians) in the same field as he sowed the "wheat" (sons of the kingdom) "while men were sleeping". The only thing stopping apostasy from taking over until the Christian scriptures were complete, was the presence of the apostles. Once they were gone, (sleeping in death) Christ's teachings were completely corrupted when pagan beliefs and practices began to infiltrate, unhindered. The weeds germinated and almost choked true Christianity out of existence....but not completely.
So, it is true, history will attest that what you said about "Christianity" being "integrated with pre-existing pagan practices" is spot on. The trouble is, that is not true Christianity, and never was. When that apostasy took over, Jesus left the church. This is why he can say at the judgment, to those false Christians..
."I never knew you! Get away from me you workers of lawlessness!" (Matthew 7:21-23)
"Never" means "not ever"....so Christ has never recognised what passes as Christianity today. It fails to reflect Christ's teachings and example in any way.
If you research what original Christianity was like, you will see that "the church" lost its way many centuries ago.
Most people don't know how far they have deviated.