Nothing really went wrong. He's had a very nice career so far.
He adapted his game in Toronto. He went from offensive defenseman who goes for big hits, to a two-way defenseman who still got caught on big hits from time to time, but played a more responsible game.
In Ottawa, he had a solid year last season against the top lines and not being the focal point. This season, everything turned to **** in Ottawa so it's hard to blame him. His skating has regressed, though.
Seems like a good fit for LA.
He came into the league and lit it up early with his big shot from the point and his monstrous hits. Then, he got paid big money, but his play didn't evolve and the opposition figured out how to play against him more effectively.
Thus, everyone looks at his contract or his past and expects more than what he is.
For any player, you have to take Samuel Jackson's line from the Captain America Winter Soldier movie:
"SHIELD takes the world as it is, not how we like it to be"
Can't keep expecting Dion to be that rookie or sophomore Dman who burst onto the scene. He's not that guy anymore, not for a while.