the op seems to wish to create an understanding of the word gospel that is actually not biblical
the word gospel itself, simply means GOOD NEWS
so what is the good news? Paul never commits to preaching any gospel save the one he came to understand after his conversion
15 Now I would remind you, brothers, of the gospel I preached to you, which you received, in which you stand, 2 and by which you are being saved, if you hold fast to the word I preached to you—unless you believed in vain.
3 For I delivered to you as of first importance what I also received: that Christ died for our sins in accordance with the Scriptures, 4 that he was buried, that he was raised on the third day in accordance with the Scriptures, 5 and that he appeared to Cephas, then to the twelve. 6 Then he appeared to more than five hundred brothers at one time, most of whom are still alive, though some have fallen asleep. I Corinthians 15: 1-6
it would not be the gospel without Christ's resurrection and the reason for the resurrection was His sinless nature
everything Paul wrote after that was either explanation or correction of this gospel and not his own