I agree, United started from a lower base although it was hardly the worse team (aging but just finished premier league winners), but if 8 years worth of multi million spending doesn't get you to your base now then i don't know what else you need.
You've spent about the same gross and way more net than the chelsea team, as well as spunking wages far higher than chelsea.
In the same time, it took city only 4/5 seasons to win the league and manager changing to, admittedly nowadays the bar has been set a lot higher
You said turning over the managers wouldn't make a difference for United, i beg to differ as you have some quality players but for whatever reason, the managers can't get them to gel (mainly cause they like to attack and you've been hiring managers who don't know how to coach the players to attack).