That's such bizarre logic. Are you suggesting that every team that has an incompetent manager, suddenly also has a crap squad? Were the majority of the Chelsea team suddenly crap under Scolari/AVB? Of course not, a managers job is to motivate his players and find a system that gets the best out of them. The difference between a crap manager and a great manager is the results and performances of a shit team vs a great team, that's the problem.
After last season a mixed team of Arsenal/United (if you are being kind to Arsenal) would have been something like:
_________DDG
Rafael Ferdinand Evans Gibbs
Walcott Carrick Arteta Ramsey
_______Cazorla
________RVP
A mixed team of Chelsea/United would be likewise balanced:
__________DDG
Rafael Ferdinand Evans Azpilicueta
______Carrick Ramires
___Hazard Mata Oscar
__________RVP
This is discounting the fact that Rooney would be in both teams if not for the worst season of his career last year.
To be honest I find it pretty disgusting that people are so quick to deem our squad terrible after the amount of trophies they've won for us in the last 3-4 years. The likes of Rafael, Carrick, Evans, Kagawa and Vidic are still comparable to the player's at Arsenal, Chelsea and City. That's before you even talk about Rooney, RVP, Mata, DDG and Januzaj who'd all be starting often for the likes of Chelsea, City and Arsenal. That's 10 player's who would be either starting often or good squad player's at our supposed rivals (before you even talk about Liverpool).
It's not that they're mentally weak, lack commitment or lacking in quality. It's that they are not being managed, motivated or directed well. They aren't just people who can be programmed to perform every week. They have to have confidence instilled in them and a system has to be in place to get the best out of them. Look at Terry, Cahill, Luiz, Hazard and Azpilicueta under Mourinho. They've gone from either past it, overrated or plain awful to producing week in week out at a team that is favourites to win the League. I have no doubt if we had a quality new manager we'd see a similar upturn in the form of Carrick, Rafael, Vidic, Evans, Kagawa etc.