Name a single time in the manga that Oda has had Luffy kill his opponent at the end of an Arc... With no precedent, the burden of proof lies on you to prove he is dead.
Again, Blackbeard is meant to surpass Whitebeard, as Luffy is meant to surpass Roger. The two share the same name as the real life Blackbeard. Teach got Whitebeards devil fruit, which contributed to WBs title as WSM. Blackbeard is geared up to be the final antagonist. Right now, it stands to reason that he is the best bet for the new WSM, which Oda has yet to name.
So headcanon, that literally goes against what you are arguing. You say only Oda can give titles, then you just make up your own rules in the very next breath that contradicts your initial argument. Mind boggling. Again, those must be some great drugs you're on... Now go sleep them off.