I overall have little issue with how Luke in TLJ was portrayed. From my perspective, Luke always had this fear of losing his closet friends whom largely became his family. It’s what prompted him to leave Dagobah and head straight into the Bespin death trap. In ROTJ, he lost his cool whenever Vader mentioned Leia. His core fear is losing anyone tragically and he tends to act irrationally whenever that possibility arises. Therefore, when it came to Ben Solo, and how seemingly one Padawan could ruin the peace he worked so hard to create, he reverted back to his instinctual fear.
You could say he should grow into a wise sage that never succumbs to those kind of emotions but I like to think he held onto those humanly flaws. It would had been very bizarre if he had actually killed Ben, but the good in Luke that is always within him stops that aggression that plagued Vader.

It’s not the Luke many of us wanted to see post-Jedi, but that’s pretty much one of the few RJ choices I could get behind. I still, however, view TLJ as a terrible middle act overall.