sorry, i didn’t read your entire post, only the first few sentences, but i’ll try to reply.
i don’t see how luke isn’t literally being ‘the last hope’ when he’s facing down the two most powerful men in the galaxy alone.
i also don’t see why luke was the hope for the galaxy and not for the jedi. i’ve always interpreted it as the latter.
i’m not being able to translate my thoughts into words well enough, so sorry about that, but meh
Luke’s only role in the final battle was one of liability. He turned himself in (an admittedly noble gesture) because his very presence put the mission at risk. So already his being a Jedi was not helpful.
Secondly his expressed desire (see the scene with Leia) was a) turning himself in for the above reason and b) turning Vader to the ‘good side’. Nothing about the Emperor or facing down the bad guys. He merely wanted to save his war-criminal father. Again, not helpful (unless your surname happens to be Skywalker).
Thirdly, while Palpatine was blowing rebel ships to smithereens with a super-laser, Luke was hiding under a staircase because he didn’t want to fight. What would you do if you had fighting skills and were alone in a room with Hitler and his bestie? Would you go meditate somewhere, or would you do everything in your power to subvert the slaughter of innocent people?