I think the general issue with the execution of Ben’s sacrifice is that it’s not entirely clear to a) the audience or b) Rey that Ben is actually, for real, going to die. Obviously by the movie’s internal force healing logical he has to, but after three fakeout deaths already (Chewie, C3P0, Rey) the audience is primed to expect this to be some sort of Force Dyad Ex Machina.
The music is tragic at first while he heals Rey, but then it becomes triumphant, and happy, and they kiss, and - oh, he dies anyway. There was just a bit of lag before the force claimed its life debt. Yes, I get that it’s intentionally playing with the audience’s emotions, but it just takes what could have been a triumphant moment of redemption (with the audience cheering Ben on to finally realise Anakin’s ambition to save others from death, but in a non-possessive, light side way) and turns into into a weird, empty guessing game.
Rey certainly didn’t expect him to die, and Daisy Ridley did a great job of making sure we can pin point the exact moment her heart rips in half, especially in eight times slowmo.