Football fans tend to completely ignore three things when it comes to comparing teams:
1) United has a big financial head start in England: in order for a mid table team (e.g. Citeh) to compete with a team like United, they need significant initial investment in the order of hundreds of millions. United, on the other hand, has spent that money over several years. Where were people when United was buying close to 10 current players who are more expensive than Arsenal's most expensive current player?
2) Diminishing returns: after a while, it doesn't really matter if you buy more and more good players. You can only field 11 players at a time and play 90 minutes at a time. Barca buying Fabregas is a good example. He hasn't really helped them because they already have Xavi, Iniesta, Thiago etc doing the exact same thing.
3) Class attracts class: A coach like Mourinho ends up at the richest squads just as the best players do. Mourinho, rich clubs and top players all want to win, so they find each other.
People who sit here and bitterly complain about each title that people like Mourinho win should remember this. To elevate a team, you need a concentrated spending boost, but after a while additional investment makes little difference.
