The filmmakers could’ve given Luke a different motivation for staying on Ahch-To, while not having him be out-of-character, contradictory to his already-established character traits (like redeeming other family members) or undoing his arc from the original trilogy so they can re-do that arc all over again. I mean, why would he be looking for the first Jedi temple, as mentioned by Han in The Force Awakens?
the fact that people think “redeeming family members” is a character trait and not an action of pure good shows that it needed to be told this way xP
it’s not redo-ing a character arc if he learns and develops further than the original lesson