“Paul’s words would include as authoritative Scripture his very own writings as he said to the Galatians that should even an angel declare something contrary to what Paul had passed on to them as good news that one should be accursed. (Gal. 1:6-10)
That’s not what he says.
“But even if we or an angel from heaven should preach a gospel other than the one we preached to you, let him be eternally condemned.”
He does not say that the Epistle of Galatians is to be considered canon. What he does say is the “Preach a Gospel other than the one we preached to you.” Why doesn’t Paul say, “The Gospel written by Luke, or the Gospel written by Matthew?” The answer is that they were not transcribed until after the Epistles were written.
The Gospels were taught orally, from the Apostles who had seen the Risen Lord, to the parishioners. They were first recorded about 25 years after Christ in the synoptic Gospels, which we currently have now, from a combination of interviews and work over quite some time.
The Epistles came first, they were copies of letters that Paul, or Peter wrote to the individual churches. Then after them came the Synoptics, and then finally, the Gospel of John and the Apocalypse.
“And count the patience of our Lord as salvation, just as our beloved brother Paul also wrote to you according to the wisdom given him, as he does in all his letters when he speaks in them of these matters. There are some things in them that are hard to understand, which the ignorant and unstable twist to their own destruction, as they do the other Scriptures.”
Ok, that makes much more sense.
Now, here’s a question. Which letters? All this says is that Paul wrote some of the Epistles, but they are never named. So what we can infer from this is that some (or all) of Paul’s epistles were written prior to 2 Peter. What this does not tell us is which ones were written (presumably Corinthians and Galatians), and possibly others. It also tells us that at least two of the other ‘scriptures’ presumably the Epistles were written by people other than Peter and Paul, and were written prior to 2 Peter.
It would make sense that he would name the Gospels, and their authors if they were written at the time of 2 Peter, but they came somewhat later.