I know what you are trying to say but it is a misapplication regarding inspiration. Paul says I not the Lord clarifying that Jesus did not teach directly to the disciples on that topic.Yes, all SCRIPTURE is unless the author says it is not scripture or inspired by God. Yes, Peter verified that Paul is indeed an apostle and his epistles are scripture. That was a general statement. Paul was specific in what is and what is not.
But Paul declares he learned everything by direct revelation from the Lord.
So your apparent argument holds no water with 1 Corinthians 7:10-12