IMO this Scripture proves Shaul was legit and shows the reason for the accusations.
2 Kepha 3:15-16, "And recognize that the longsuffering of our Savior is salvation; just as our beloved brother Shaul, in
accordance with the wisdom given to him, has written to you, As also in all his letters, speaking in them about these things, in which are some things hard to be understood, which those who are unlearned and unstable twist, as they also do the other Scriptures, to their own destruction."
Shaul was educated by the Pharisiee and roman schools, if I remember correctly the school of Tiberius, so his worldly education was beyond any of the other writers of the Scroptures. He writes in a way that is hard to understand, I think all can agree when first read Shaul's writings they must be read over and over to grasp what he is saying, and looked at as not changing anything but supporting what Yahshua said and did. I think to try to understand his words outside that context is certian error. Yahweh inspired Kepha to write this passage about Shaul's words being easily misunderstood, I think this has to be taken into consideration when studying. I do want to add that IMO most churches these days almost exclusively read Shaul and ignore the rest, which creates fertile ground to twist his words, and what happens is people carry these false interpretations on and then others know these are false but then point to Shaul being false insted of correctly putting the blame on misunderstanding.