I'm going to be found hiding under a rock, beaten to a pulp and tossed into freezing water for this, but to me Rooney wasn't world class. He should have been, but imho he never quite reached that height.
He had all the tools in his early years to be world class, but in his teens he was hot tempered and a little inconsistent, and unfortunately his inconsistencies carried on. Even in his best seasons he was always a little patchy, and when he was about to hit his prime, his body started to let him down a little. More accurately, he started to let his body down.
In RvP's last season at Arsenal and first season at United, he was the better player of him and Rooney. After that, Suarez (pains me to say it), Aguero were better than Rooney. Before that, you had Drogba, Henry etc who were better. He was never the best striker in the PL, although he was considered one of the best players for several seasons, rightly so. One of the best does not guarantee you world class recognition though. For me, he just isn't quite there.