Luke did something we’ve never seen any other Jedi do before. He projected a solid version of himself across unimaginable distances and could interact with Leia and even Threepio. That had to come with a price. In the end, Luke saved the day one last time and went out a hero.
I didn’t get that from the movie at all. If that had been communicated more clearly to the audience it might not have felt so insulting to me.
I think the whole reason why there was salt on the ground was so that they could show us that Luke isn’t real in that scene. Plus, it was flashback Luke using a lightsaber that had just been destroyed the scene before. Unless you’re talking about the philosophical meaning of the scene instead of the literal; if so, I’m sorry for the inconvenience.