They were immature, but they did not, to my memory, pull the team down with them, rather, they contributed to a winning teams (if not always contenders) thus were on balance positive forces for their teams, despite all their problems. (I may be remembering incorrectly but don't have the time to source check myself.) Cousins, in contrast, is a main contributor to the losing/negative environment in Sacramento. He's had several coaches, many teammates, management changes and an ownership change, yet nothing ever changes in terms of outcomes. He's the one constant to all the turmoil and losing in Sacramento. At some point, you really need to stop pointing the finger at everyone and everything except Cousins. He's a major part of the problem, I don't see how anyone can deny it at this point.
Your arguments seem to be to be like you're defending a guy who's been married and divorced multiple times arguing that all he needs is the perfect wife in the perfect situation and the next marriage will finally work. By this point, however, it's hard to escape the conclusion that it can't always just be the wife's fault, he has to bear some blame as well and probably a good share of it.
I think the better example for you is Zach Randolph. This is a guy who was a major head case early on and turned it around. So, I suppose it can be done. I have no insight into Cousins' psyche, I can only judge by what I see repeated over and over and over again. I could be wrong, I am not a psychologist, I only play one on Jazzfanz.