The Pauline Epistles held in less esteem than the synoptic Gospels? By whom? And if so, to what extent? It seemed another of those manufactured arguments. They just keep coming.
In comparison, those OT books Luther moved to appendix did have some long (albeit not entirely universal) history of being held in much lesser regard. We do not see the same for Paul's letters, well, until perhaps by papal decree Paul became declared to be subservient to Peter? -- and if any disagrees with that, then anathema upon them.
To cover that sort of thing with the "this church among all others alone, has never erred" thinking, is just so much after-the-fact justification or cover-up.
Let us all return to the more and most original articles (of faith) please...
What is obviously overlooked is that the SAME Holy Spirit brought to the gospel writer's remembrance all that Jesus had taught them ALSO moved the rest of Scripture's writers to write what they did. Paul certainly wasn't just going by the seat of his pants (robe?) here, he was writing what GOD told him specifically to write and, as Daniel1212 has said many times, those words had power behind them to change a person's very life and eternity. Scripture is "alive and active. Sharper than any double-edged sword, it penetrates even to dividing soul and spirit, joints and marrow; it judges the thoughts and attitudes of the heart." (Heb. 4:12). Somehow, I just don't get that same vibe reading "I also will here make an end of my narration. Which if I have done well, and as it becometh the history, it is what I desired: but if not so perfectly, it must be pardoned me" (2 Maccabees 15:28, 39)."