Isaiah Thomas would be another one as he got minor MVP consideration after his best season before injuries derailed his career.
DeMarcus had one great year alongside AD but you can't really say it was significantly better than what he did in his best seasons as a King. And while he may not have had the injury issues had the Kings not traded him, if he did Sacramento would likely still be paying him supermax money right now.
Thomas Robinson, Jimmer, Stauskas, and Papagiannis were all out of the NBA after a few seasons. McLemore, WCS, Justin Jackson, Harry Giles, and Skal Labissiere are all deep bench players and/or barely hanging on to an NBA career.
And those are just the first round picks.
IT clearly played better just after leaving the Kings. Bogdan is debatable. He looks the same to me, just playing on a better team that uses him well.
But to me the most glaring thing is how awful the Kings have been at drafting overall. It's absolutely critical for such a small market team to build through the draft (OKC, San Antonio, etc) and the Kings have just botched it most years. The Warriors picked after them in the years that they got Steph and Klay. The Kings missed out on Kawhi, Lillard, Giannis, Booker, Luka, and that's again only counting first rounders and not 2nd round outliers like Jokic or Draymond.
The problem isn't Kings players leaving and then improving. It's not getting good enough players to begin with.