I don’t suppose you read the entire verse. It gives the entire recipe then says it’s perfect and thoroughly furnished unto all good works. Why would you then compare it to a cake and use just the flour part? Is the cake perfect and thoroughly furnished to become a cake with just the flour? "ALL SCRIPTURE is given by inspiration of God, and is profitable for DOCTRINE, for REPROOF, for CORRECTION, for INSTRUCTION IN RIGHTEOUSNESS: That the man of GOd may be PERFECT, THOROUGHLY FURNISHED unto all good works." 2 Tim. 3:16-17.
Paul wouldn’t have used the words
perfect, thoroughly furnished if he was talking about just the flour part of a cake. He was showing the “cake” would be a perfect, thoroughly furnished to be a cake. Catholics can try to twist the words all they want to try to God’s word to no avail in an attempt to justify the “doctrines of man” from the RCC but it’s still “doctrines of man”.
Is the cake perfect and thoroughly furnished to become a cake with just the flour? "
Nope even though flour is profitable or useful for a perfect cake.
Is the doctrine, etc. perfect and thoroughly furnished with just scripture?
Nope, for the same reason. There's just no way to make profitable or useful mean "all that's needed" or "entirely sufficient."