Of course it's an exaggeration, but rooney at 18 was much more exciting, unpredictable & had the talent to become the best player in the world.
He burst onto the scene, looked great and the English hype machine turned him into the best thing since Maradona. He went to one of the best teams in Europe for attacking talent to flourish and has been hugely successful - I can't see any "what ifs" in the case of Rooney.
He's never looked short on desire or commitment and the argument that Ferguson played him out on the left or wherever doesn't wash either. Zidane found himself out on the left wing at Real and many other top attacking talents have found themselves playing where they're not quite at their best.
He was never going to become the best player in the world because the likes of Messi and Ronaldo were always going to be better and the no-one else in England really saw that coming. Ending up in the second tier during an age when arguably a couple of the greatest attackers ever to have played the game are at their peak isn't really anything to be ashamed about.