Paul makes the claim that he received his information directly from the risen Lord (Gal 1-2). Paul was sent to us, the Gentiles, (Acts 22:14; Acts 26:14-18; Rom 11:13-15; 1 Cor 9:1, 16-17; 2 Tim 1:11; Titus1:3; etc, etc) + with the message of Salvation by Grace, through Faith. Jesus was sent to the nation of Isreal, he taught people to keep the law. It wasn't until he was rejected and crucified and the nation of Israel was given the final chance in Acts to accept him as their Messiah, that God raised up Paul and set Israel aside. Acts 13:38-52
If you look at the Scriptures from a dispensational perspective, virtually all of the seeming contradictions are resolved. Paul says to "follow me" (1 Cor 11:1), the revelation that he received was something new, it wasn't in addition to anything that had been taught before, it was new and it was directly from Jesus himself, therefore it supersedes what was taught prior (Eph 3)
Some day, God will deal with the nations through Israel again. Now, we are in the dispensation of Grace where God deals with us each as individuals, through faith in the accomplished work of Christ, regardless of our affiliation with Israel.
To denounce or discredit Paul is anti-Christian and it is exactly what the Jews of his day worked hard to do precisely because his message was against all that their religion had taught. Jesus was a Jew, he kept the law. Paul taught Grace and he was persecuted and killed because of it.
Here is what Peter has to say of Paul: And account that the longsuffering of our Lord is salvation; even as our beloved brother Paul also according the the wisdom given unto him hath written unto you; as also in all his epistles; speaking in them of these things; in which are some things hard to be understood, which they that are unlearned and unstable wrest, as the do also the other scriptures, unto their own destruction. 2 Peter 3:15-16
The other thing that astounds me is that if parts of the Bible are erroneous, then how can we trust any of it? Disavowing parts of the Scriptures makes a man, or a man's opinion, the final authority. If any of it is unreliable, then none of it can be trusted. This is the exactly the tool of the devil, to make each of us "god", determining what we reject or choose to believe.