It wasn't "crazy" at all, if anything Rooney was proven right. We lost Tevez and Ronaldo and Hargreaves (to injuries). Valencia was supposed to be a replacement for CR7 and washed Owen was supposed to be a replacement for Tevez. Do you really think those transfers were good? No, they were abysmal in fact. In the midfield, Scholes was getting older and we only bought Cleverly who was average at best. We still had to rely on a 37 year old Scholes and even older Giggs in the midfield. We were only a very good team because of the genius of Sir Alex. The moment he left and Moyes inherited that same exact squad (Scholes retired and Fellaini arrived), we finished 6th in the Premier League.
So technically we were the second best team in the world behind Barcelona, but it was obvious how much better Barcelona was against us. Why? Because they kept buying superstars and better players. For example David Villa and Ibrahimovic. Henry before that. Our only notable purchase during that time was the purchase of Van Persie. And it ends there. The Glazers didn't properly back Fergie in his last couple of years at Utd and he left us an aging squad that needed to be rebuild. Basically, Fergie was papering the cracks that whole time. The results were great, but if we had a proper backing there would be a couple of more Champions Leagues. Now, does that justify the behavior of Rooney? Not really, but you can't say that he was talking bollocks.