“They do not need an affirmation from Paul.”
Correct. But He in fact CHOSE Paul as an apostle and taught him through personal revelation, personally setting him apart as his minister to the Gentiles. So it really is Christ speaking to us through Paul, after his resurrection. If you don’t believe that you just lost at least 13 letters from the NT (Hebrews’ authorship being in dispute).
No one is denying the authority of Paul. Rather, the point is that the sayings of Jesus stand on their own and do not need Paul to be confirmed.