The execution of Han Solo’s character in Return of the Jedi is not perfect, and somewhat far from good/what it should’ve been with the message they were trying to say.
But he wasn’t contradictory to his character in the other movies like Luke is in Star Wars: The Last Jedi in any way whatsoever.
If I may amend your argument: The idea that Luke is a broken, haunted man 30 years later could work. The idea that he became so only within the last few years because he lacked the wisdom and control to deal with a relative tempted by the dark side is not terribly convincing. That part is, as you say, contradictory. Beloved characters can be taken in directions we may not love, but there is a greater call to have it be convincing. A moment of madness followed by total capitulation doesn’t line up with Luke at the end of ROTJ, absent more than Ben’s flirtations with the dark side.