You're pretty good at identifying the problem . . .
OK.
Paul did not say that he would lose salvation, in this you are correct.
However, Paul did not say that he would be disqualified from the wedding feast of the Lamb. And he did not say that he would be a "vessel unto dishonor". He didn't say these things. These are your own conclusions, but I really don't see them based in Scripture.
IN those places where you see this taught, I'd be happy to look at them one at a time with you.
Much love!
Paul did say he could become a castaway in 1 Corinthians 9:24-27.
Jesus said He would cut off those from the vine for not abiding in Him; John 15:6
Jesus also said He would cut them asunder to have their portions with unbelievers in Luke 12:40-49 in facing the calamity of fire coming on the earth.
That is what Peter was warning believers to be saved from that calamity of fire by enduring to the end in 2 Peter 3:3-15