Anyone who says Cousins should go before PW is an idiot. But a better thing to do was to round up the guys, and if they all feel this "System" isn't working then go to the coach or assistant coaches about it as a unit. Getting all ****ed off and "demanding" a trade when you're one of the core young guys is not good for the team. If I were Cousins' team mate, even if the coach got replaced I would be worried that when things went south Cousins would just try to bail and not stick with the team.
And like people have said, Cousins hasn't done anything to give him this sort of authority to demand a trade or act like he's the biggest honcho on the Kings. Say what you want about the system, but in this short season he hasn't played well individually at all, missing lots of lay ups, not getting back on defense, taking a lot of outside jumpers.
The guys were optimistic going into the season, and clearly had some faith in the implemented system. I don't think that it's rational for a player to start demanding a trade after losing 3 out of 4 games. Sure, there's reason to be upset with the coach but if you intend to be a likeable guy in the league this is not the way to react.