Luke did act out of character - for someone who risked his life to pull the light out of darkness then turn around and attempt to murder one of his students because he saw some darkness didn't make sense - especially with treating the whole thing in a 2 minute flash back.
But it wasn't just Luke - it was the trashing of the entire concept of the Jedi Knights and the light side of the force while giving the Sith a complete pass and all of the established lore and history as Rian flipped the fandom the bird. It might've even been given a pass if the story had been decent - but it wasn't even that. They still haven't established what the First Order IS in the galaxy except for the fact that it seems to have taken over the thousands of worlds in the Empire and all the rich people are perfectly happy with it while the resistance (helmed by the people that destroyed the Empire) grow weaker and weaker. But for all the vaunted power the First Order doesn't seem to understand basic military tactics like ordering a few ships IN FRONT of the fleeing resistance ship to cut it off at the pass.
MEANWHILE there doesn't seem to be any problem of having a shuttle take off and get away AND THEN COME BACK into the middle of a warzone with not one attack on it (golly, maybe they should've come back with multiple shuttles and flown the rest of the crew off!)
I'm not a perfectionist in storytelling by any means (C'mon... Ewoks... really?... but you have to get me to suspend belief and at least be entertaining)
To top it off - Disney seems hellbent on misunderstanding what Star Wars is with this inspid "end of the skywalker saga" nonsense. Star Wars was first and foremost a homage to SERIALS. Short (30 minutes or so) episodes to run before a main picture at the theaters, do some entertaining things and then hook you at the end to come back next week. You don't NEED to relate everything to Luke and Darth Vader but you can't retcon the storyline because its central to the mythology. Even Lucas understood that, which is why he wanted 7-9 to be about the journey of the Whills. But if you destroy that storyline there's no anchor to the Star Wars universe and you just have "Space Disney... with magic lightsabers!". The ultimate irony here is that they didn't HAVE to use the old characters - Episode 7 could've easily started 200 years after the fall of the Empire and gone from there but Disney wanted the easy cash but doesn't want to be beholden to the old mythos. Why? Because they don't want to pay licensing fees to Lucas?! Geez, PAY Lucas the licensing fee and use the original characters then use your "star wars stories" to test market new characters until you get one that works then phase them in and phase out the old characters. Don't kill the golden goose trying to get all the golden eggs at once!
The more you tighten your grip, the more dollars will slip through your fingers!