It ends the same way everywhere he goes, and we (including me) just excuse him with some variation of: "It's okay that he's acting like a petulant child*; he just wants to win so bad, and the franchise he's with is full of losers."
Those Finals appearances were in the post-LeBron East, he had a little injury luck (KD and Giannis) and the Celtics still hadn't figured things out yet...but I give him and those teams full credit for getting hot and making their runs, and Jimmy has some absolutely incredible, ballsy postseason performances to his name.
But, at some point, he's an 18, 5, and 4 guy who has played over 60 games twice in 8 seasons, who maxed out as a fringe top 10 guy at his peak. If he was a true superstar, he would be getting pummeled for his repeat history of blowing things up. But he's a 2nd or 3rd tier guy that everyone kind of likes, so he gets away with it.
Would I want him on my playoff team at a reasonable number that could be moved when things went sideways? Fuck yes.
Do I want him as the leader and best player on my team? Fuck no.
*usually over a contract dispute, not team performance