"It always amazes me how many arguments against Christianity base themselves on things that are NOT Christianity."
I find this remark typical, and it wreaks of confirmation bias. You cannot discern truth by examining only 1 side of the story.
There are numerous reasons to disbelieve Christianity. I finally saw "the light" after 20+ years of drinking the koolaid. As to the validity of Paul being a legitimate apostle, read Jesus Words Only by Douglas Del Tonto, and about how the Council of Nicaea (i.e. Constantine) orchestrated the Cannon in 325 AD see God's Secretary by Adam Nicholson Those are only 2 example of works that tainted the sweetness of the koolaid that ultimately led to my epiphany that religion is the same as government == a means of controlling the masses. Another extremely important work is The Most Dangerous Superstition by Larken Rose. The later applies not only to religion but any hierarchical organization that equates labels of authority with trustworthiness. Better to train yourself in the skills of critical thinking using the Trvium Method.
Every time I see that Council of Nicaea argument I know who's been drinking the Kool-Aid. You got that from Dan Brown's DaVinci Code no doubt - full of false information that people scoop up and spout back. The series of councils that debated which texts were authentic and which were not took place over many centuries and the final official canon was not universally accepted until about 500 AD. The texts themselves were not edited in any way during this process - they just had to prove that they were authored by an apostle or an apostle's assistant to count. Very reasonable due diligence.
And if you find my remark typical, I'm surprised but pleased. I would hope that all Christians could articulate this. Still it is clear to me you didn't understand what I said. That statement is arguing that critics of Christianity are picking on strawman actions and incorrect beliefs that are not part of Biblical Christianity. That's a simple statement and has nothing at all to do with confirmation bias or examining only one side of the story. I'm saying that criticizing something that is not in the Bible is criticizing something that is not Biblical Christianity. Simple.
There can be no doubt that Paul was a legitimate apostle because all the other apostles and the Christian communities of his day accepted him as such. John outlived him by several decades in Ephesus, right smack dab in the middle of Paul's missionary heartland. If there were false teachings from Paul, John had plenty of time to correct them.