No, he is not. He was the 10th pick and he isn't halfway through his first season. You can't begin to call him a bust until year 3 at the earliest. Even still, a bust with the 10th pick is not really a bust.
I agree with your general point, but I think we can put 1+1 together on what a guy will likely be, before year 3.
Xavier Henry, for example. He's in year 3 and I think the writing has been the wall for him for a while now. He'll be a guy that has to hang on to stay in the league.
He's also had a really similar basketball arc to Rivers. One of the 2 or 3 best players in his HS class. Went to Kansas for one season and like Rviers, somewhat under performed people's expectations. Then was drafted 12th overall. People gave up on him long ago. His own team did. Its why I don't believe for one second, even Rivers' biggest supporters will actually still be giving him slack in year 3.
Oh and Aminu's in year 3. He went 8th overall. Do we really need more time to make a determination on him?