If he was that unhappy he could have threatened to walk if changes weren’t made. It’s not like they could replace him.
And that’s hardly blasting the director.
He was hired to do a job, and so he did that job to the best of his abilities, and to his credit it’s an amazing performance. He doesn’t have to like it though, as he clearly doesn’t. It’s RJ’s vision for the character and he respects that, but he doesn’t feel that character is Luke Skywalker.
And lest we forget, Harrison Ford had issues with George over not killing Han off in ROTJ.