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.
Maybe we had never seen this before because it makes alot of things obsolete.
If the jedi (and throught the time there were a lot of jedi more powerful than Luke) could project a solid self to anywhere in the galaxy they could enter enemy ships ore bases and sabotage it or so. Many things in the war would be handled differently.
This solid projection reminds me of the transwarp beaming in ST:Into Darkness.
An invention that makes the entire Starfleet pointless. Why not let Luke come to the battle in person and die like a hero? Not like “go to sleep on a dank rock!”