He does make a nice long term fit - for Golden State, NY, Miami, Atlanta. He'd be great for those teams long term. Just not for the Kings, long term. He's a nice stop-gap for the Kings to fit in while Cuz is learning the ropes and maturing, and in certain situations in which he and Cuz can match up because they don't have to match up with a pf who has some quicks and an outside shot.
Why is he long term for other teams and not the Kings? If he fits in good with Cousins now why change that?