There was no Christianity during the time of Paul. The movement was still Jewish, so it would have been virtually impossible for Paul to actually do something with Christianity.
On a side note, the teachings of Paul do make a foundation for Christianity. So Paul is needed for Christianity.
"There was no Christianity during the time of Paul"?
What do you think the Apostles were teaching? What were they seeking to win converts to?
Nazarenes, or Hebrew Christians if you prefer, but either way
Christian.
James, brother of Jesus, was the first ruler of the Christian Church in Jerusalem....
You are perhaps getting mixed up with Roman Catholicism. That didn't come into being until the 4th century. Though the creed of Roman Catholicism is Churchianity, not Christianity.
Paul was the arch-enemy of the early Christians. His later 'conversion' was nothing more than a ruse to destroy Christianity from within. [He was to lead a meat-eating schism against true Christianity, being vehemently opposed to nearly everything it stood for.]
In the Clementine Homilies there is a record of how Paul ambushed James and his Christian brethren in the temple, and incited the crowd present to set upon them and tear them limb from limb. Paul is recorded as personally violently assaulting James, savagely beating him and throwing down the temple steps and leaving him for dead.
And Church doctrine is centred on Paul!
There's more Paul than Jesus in the Bible New Testament! And what has Paul to do with anything anyway? He never even met Jesus.
Besides, even many pro-Bible scholars acknowledge that some of the Pauline Epistles weren't even written by Paul and that those that were suffered later interpolation.