We understand the difference clearly and people were saying it as early as 2005.
Chelsea, and subsequently Man City, are clubs plucked from relative obscurity and pumped with billions to try and win trophies for some billionaire's football fun. United are the opposite - a club with a phenomenal success story which built them into an iconic brand, so were instead bought to be a cash cow for some billionaire who has no clue about football. That's been the difference in "focus".
We were fortunate enough post 2005 that, players we broke the bank for pre-2005 when we had ambition to get the best talent like Rooney, Ronaldo and Ferdinand, were still awaiting their sensational primes and we were able to compete with Chelsea and were more successful than them. We were also lucky that Giggs, Scholes, Neville and Ferguson had some gas left in the tank and that Fergie and Gill still had such an eye for talent when making cheap signings like Vidic, VDS, Evra, Park and Carrick. We were of course very lucky that Fergie was such a genius that when that team got older and some players left and we got the point where we were constantly missing out on the best talent (Hazard the best example) he was still able to deliver titles with more average United sides.
Now he's gone, those players are gone, the eye for talent has been replaced by commercially focused / panic signings when we look like we won't make the top 4...look where we are. Unable to compete with Man City for 10 years. Things may improve long term under SJR though and we look like we are at least trying to move back into the other direction.