The story and universe is very deep full of lots of lore and stories even in places irrelevant to the story line and beyond the current shown map. But even if you were to take the Azor theory as destiny and unstoppable fact Jon isn't even the most fitting character for it, Dany is.
I also see why the pieces could align for Jon but how is confirming that theory good writing? It would just confirm he is Azor and then give you a drama free storyline where you know he is going to win because destiny says so.
As far as Mel goes like I said I still don't see why everyone is head over heals for her. Unless she was playing Stannis from day 1 to get to Jon (not utterly impossible she once gave a very cryptic quote about a sheep and its awareness of the blade under its throat, I forget the exact quote) then Mel misguided the entire time and showed how pointless her views are by backing Stannis as Azor.
As far as killing Snow at this point it goes along entirely with the story. A story that has established that anyone can die, fail, or disappear no matter how much development they have or how long they have been on the show. At this point it seems silly to think more big characters wont be dying next season and the one after.
Of course I could be wrong and Snow may get revived I certainly dont write the story but to me the story is better off leaving him dead and not raising him like some unstoppable Jesus who is going to save the world and fill a prophesy.