Still no idea what you think was missing from the explanation of how he got there. Him being there was a given. It awkwardly ended the previous movie, with a bizarre helicopter circle shot. Sprinkled throughout two whole acts, we got a Rashomon overview of him doing what we expected and having that blow up in his face. Short of making the movie about him–
And we’re glossing over how Luke in Return Of The Jedi very nearly turned to the dark side. The Emperor was fuckin’ thrilled until he got chucked down that elevator shaft. Luke Skywalker was always a hold-my-beer archetype. Plan A for Darth Vader was murder. There was no Plan B. Even with Jabba and the Emperor, his idea of a diplomatic alternative was to surrender his way in, and then murder his way out.
Luke being grumpy is infinitely more explicable than having the empire ‘return, somehow.’ Especially for an audience that’s spent decades joking about the prequels, and wonders if the whole franchise would’ve gone better if Qui-Gon hadn’t yelled “duck.” Having the prescience to see Kylo ruin everything is the fuzzy precognition we’ve long since known about. Seriously considering murder as a solution is his go-to. He’s not Batman.