Interesting. See I take the exact opposite approach, that it's completely pointless killing someone off unless you spend time building up the character.
Also you can say it's bad storytelling, but you can't say it wouldn't be unexpected. Even after we saw Jon get stabbed to death everyone is expecting some manner of either non-fatal injuries or miraculous resurrection. Him remaining dead would be maybe the most unexpected event in the entire series. You yourself expect him to become a dragon rider and last until the final battle, although I'm slightly baffled as to why you think it'll be at the Trident. Do you think the Others are going to get that far south?
It depends on the timing of it. Jon dying at the final battle would make sense storytelling wise. I actually hated Harry Potter's fake out death and thought it would have been interesting for him to really die during the final battle. However, that is during the final battle - as in the ending of Book 7. It really is bad writing for Martin to kill off his lead character two books before the story has ended for no reason. Strikes me like something that a high school/ college student taking their first creative writing class would do just because they wanted to do something that no one else thought of without considering the plot or character development.
Both Ned's death and the Red Wedding were shocking, but made narrative sense in the story. Ned was the Obi Wan Kenobi mentor figure and his death kicked off the stories of his children, the real main characters. The Red Wedding was more shocking for how Robb/ Cat's deaths happened rather than that they happened. Even the unsullied are predicting Robb's death. Jon is the main Stark who is going to be thrust into a leadership role, so Robb had to die. It's the same argument for why Aegon isn't real. Jon and Dany will be leading the final battle against the Others, so all other potential leaders have to die.
As for the final battle, I most definitely expect it to be on the Trident. Dany has a dream of fighting on the Trident in either ACOK or SOS. And Jon will likely go south after his resurrection and meet with Howland Reed. I expect Reed and Melisandre to play good mentor/ bad mentor.