"ALL scripture is given by God, and is profitable for doctrine..."
* * * DOES NOT EQUAL * * *
"ONLY scripture is given by God, and is profitable for doctrine..."
This Timothy passage indicates that scripture is certainly one thing "given by God" that is "profitable for doctrine.." and does NOT exclude the notion that there are other things that are "given by God" that are "profitable for doctrine..."
You completely ignored the words "throughly furnished." If, by scripture, the man of God is throughly furnished why is there a need for anything else?
He instructs us to "stand firm and hold to the traditions which you were taught by us, either by word of mouth or by letter" (2 Thess. 2:15).
We still have the letters, but does anybody now what Paul said. Could you let me in on the secret?