There was rather more to it than that:
https://www.cbr.com/last-jedi-mark-hamill-reaction/I see he's backtracking somewhat now, probably because he doesn't want to blow his chance to come back as Ghost Luke in the next one.
Quote:
“I said to Rian, I said ‘Jedis don’t give up’,” Hamill explained in an interview currently making the rounds on YouTube. “I mean even if he had a problem, maybe take a year to try and regroup… but if he made a mistake he would try and right that wrong, so right there, we had a fundamental difference, but, it’s not my story anymore. It’s somebody else’s story, and Rian needed me to be a certain way to make the ending effective.”
“That’s the crux of my problem,” he continued. “Luke would never say that. I’m sorry. Well, in this version, see. I’m talking about the George Lucas Star Wars. This is the next generation of Star Wars, so I almost had to think of Luke as another character. Maybe he’s ‘Jake’ Skywalker, he’s not my Luke Skywalker.”
Nevertheless, despite Hamill’s obvious frustration, he would go on to say, “I still haven’t accepted it completely, but it’s only a movie. I hope people like it, I hope they don’t get upset, and I came to really believe that Rian was the exact man that they needed for this job.”
Hamill’s concerns with how Johnson chose to depict Luke in The Last Jedi are well-documented. In an interview back in May, Hamill noted that he told Johnson, “I pretty much fundamentally disagree with every choice you’ve made for this character.” He would downplay those remarks the following month, but even at a press junket just days before The Last Jedi‘s theatrical release, Hamill would reiterate that his and Johnson’s vision for Luke simply didn’t line up.