The characterization of Luke in TLJ has a lot of problems, but his lack of combat isn't one of them. Luke spent the entire film trying to point out that the galaxy is too complicated for every problem to be solved by just running at bad guys with your murder-stick and beating them into submission. It would have been gay for him throw those principles away at the end of the story just for the sake of fan service.
Yeah the last part actually was Luke.
The same Luke who threw away his Lightsaber in front of the Emperor.
The rest of the film was not Luke. Having created this darksider, no attempt to reform him like he did Vader. Just hiding from his responsibilities. Thats not what a Jedi Master does.
And everything he went through to become a Jedi hes just throwing away by giving up on the Jedi. All because somebody else has turned to the dark side now. Except this time it was under his watch. Which just makes him a hypocrite for arguing with Old Ben about there still being good in Vader.
Ugh.