While Luke was jarring, especially given who we last saw him as in ROTJ, I thought the character fit, and I thought it was absolutely the best performance that Mark Hamill has given that I've seen (admittedly, I've not watched Corvette Summer, and it's been a long time since I saw Slipstream...). Hamill may also have been jarred by the tone of the character, but he knocked the performance out of the park and completely sold me on where Luke was. When I watched the film -- both in the theater and on home media since -- I never feel as if it's "Mark Hamill as Luke." It feels like "This is Luke, if these events happened to him and if he made these choices." And that's entirely due to Mark, Rian's direction, and the writing. I get why people find this characterization jarring, even shocking, but I think it fits if you can accept the critical moment at the Academy between Luke and Ben as something likely to happen.