Two MORE points you need to understand.

Where does Paul say that the other Apostles preach a "false gospel"?

He doesn't.

If Paul really thought that, he would have disassociated himself from the others.

That didn't happen.

...

John lived 30+ years LONGER than Paul did.

IF Paul was the ONLY one with the 'true gospel' as you claim, this wouldn't have happened, and Paul would have been the LAST one to die.