Absolutely the scariest thing. Obviously I’m not talking about the immediate threat, but I don’t think there’s much doubt that Kylo brought Luke more pain than Vader (I’m talking emotionally here).
I disagree. Vader in the end of TESB destroyed everything Luke believed in and everything in Luke’s world. He had possibly killed his best friend, told him that his dad was not a hero but a monster, made him see his master were liars, destroyed his base at the beginning of the movie, killed several of his friends… and Luke was a young, immature man (if you compare to what he should’ve been in TLJ).
So I highly doubt that the possible future he saw was worse than this. As selfless as anyone may be, we are always biased towards ourselves.
There’s a big difference between being 20 years old and falling on your ass and learning your dad’s a failure and being 50 years old and facing the possibility that you’re a failure and your life’s work has been meaningless.