You're right. I'm just not sure I buy it.

My issue is her relative strength compared to previous Jedi.

Look at what Rey does untrained. In Force Awakens - she uses the jedi mind trick successfully on a guard. She successfully resists kylos mind probe and indeed reads his fears. She defeats Kylo in a duel.

I'd let the defeat go cos he was probably concentrating using the force to keep himself alive after Chewie's crossbow hit - but no one has done stuff like the Jedi Mind Tick and resisting a mind read untrained before. It's basically almost the level of strength luke has in Jedi after completing his training. She's doing it untrained.

If it's because Kylo is so strong, does this mean he's stronger than Vader seeing as she appears to be proportionally stronger than luke?

Basically I was going to let it go if it turns out she's a skywalker or a kynobi or someting. But if she's a junk trader from nowhere its odd that she's the most powerful jedi ever, even than the 'chosen one' anakin and even than his blood relatives.

After the battle we see you're right about the projction - he's still on the island meditating on the rock where he was training rey. After he projected him self he collapses gasping from the effort. We see him sit up. He then gets a tranquil peaceful look as he watches the twin sunset (a nice callback to the early look shots of boy-luke looking at the setting suns in A New Hope. We then see him disappear. Similar to the way obiwan does when struck down, and basically the same as the way yoda did. Like just kinda fade and not be sitting there anymore. We also see his robe blow away into the air.

It then cuts to leia doing one of her "I'm feeling something in the force" faces, and rey kinda pauses for a moment. Later right near the very end they say something about how they felt him pass (forget the exact phrase she used) and they were like "it wasn't upset or painful, more like he found purpose and fullfillment" or some line to that effect. So yeah you could look at it like he worked himself to death with the force, but I think it's kinda that he became one with the force as it was his time having saved ray from Kylo.

Torn on it. I guess this trillogy has to be about the new characters. And I don't mind them writing him out generally. But it was sort of a bit antilclimatic after his big trick on Kylo that he ended up dying anyway.

the first movie sort of set up a few things that were mysteries that it seemed would be explained in the future instalments. Then this movie actively undid them. Which I found kinda weird.