United did that and then some. They are a Godly football club.
Even with Ronaldo and Messi and Madrid and Barca respectively, they STILL can't topple United as THE giant of world football when they are struggling in 7th place with David Moyes.
Imagine United were lucky enough to have Messi come through THEIR ranks.
It would be like cheating they'd be so dominant, so far ahead of everyone else it wouldn't even be a debate.