I think the whole contract extension issue got in his head this season and has affected his game.
Inclined to agree with you, but also worth considering that he's still improving - while he's taken a slight step back from last year overall his floor is still higher than what we saw in his rookie & sophomore seasons.
I agree, he is better than he was as a second year player. Does that necessarily mean that he's still improving, though? He wouldn't be the first player who reached his ceiling as a third year.
Also true - he may just be a guy who can give you a per 36 statline of 11-6-3. He is rebounding and passing more this year, which is good, even if his shooting has taken a hit and he's overall less effective on offense this season.
I think it depends on how much stock we put into his cold spells & hot streaks, and whether we think they're aberrations or indicative of his overall play. I'm not in love with his game, but I don't see much either way to be sure if he's peaked just yet.