I don't think having the best midfield necessarily dictates who wins the league, United have gotten away with having a good but not great midfield for the last half a decade and instead focus on having midfielders who suit their style of play by being able to spread the ball wide and chip in with goals with the space available. Arsenal, Chelsea (with fit Essein) and City (with Yaya) have had consistently more powerful midfields with better ability to keep possession but still they always find themselves being the benchmark to surpass.
Chelsea have 5 players who can play the deep lying midfield role (6 if you include Ramires), 3 great playmakers (again, 4 if Ramires plays in that right attacking mid role), and 2/3 wide players to mix things up, on paper that is one of the best groups of midfielders in the world, let alone the league (only Arsenal have better to me, City are about equal).
As I said, the midfield area has become far more important in the last few years. Man Utd have had a good midfield the last few years imo. Scholes, Carrick, Park, Fletcher and Giggs has been a revelation since he adapted his game. This year they will probably be going with Carrick (a great passer) and Cleverley, a great young modern kind of midfielder. It's evolving and a change was needed.
Ramires isn't a holding midfielder, he's only played there a couple of times (the away leg against Napoli was his last, he got torn to pieces). Mikel goes through periods where he is decent, then others where he is a real liability. Meireles has been at his best when he played as a number 10 for Liverpool and the start of last year with Chelsea. When he plays further back he's not great. Essien is essentially done unfortunately, it's no fault of his own and he will always be special to Chelsea fans, but his legs just don't have it anymore. Lampard is ok and will be useful again this year.
I agree that we have great playmakers, Mata, Hazard and Oscar is arguably the best around, the wide pacey players are getting there (Marin will be very important this year and Sturridge maybe?) I love Bertrand on the left wing, he's one hell of a player for me. Cole was injured a bit last year and he did a great job, he was man of the match in the away game against Arsenal and was huge in the Champions League final. I've said before that it was no coincidence Munich scored at the back post from a ball in from the right, just after Bertrand had gone off. Even in the Community Shield he changed the momentum and gave us a real chance to get it back level. Moses would make me happy with the wide areas (him, Marin, Sturridge and Hazard/Mata).
I just really don't think we have what it takes in midfield, which is where it counts these days. Would Messi be as great without the midfield behind him? Would Ribery and Robben get the platform to perform without Schweinsteiger behind them? Would City be as great without Toure doing everything he does? I don't think they would personally. We saw in the Euro's how a fairly average Italian team looked brilliant when Pirlo was at his best.
I think the 3 wins all season against top 10 teams (so 18 games) is such a telling statistic. Against Fulham for instance, we struggled in both games. Dembele and Murphy are built for modern day football. Our midfield is essentially the one that was good 5-7 years ago. Things are different in todays game. You see average teams like Swansea doing great things with a modern midfield. I'm not saying the players we have are no good, they're great in their own way, just not for the way we need them to be. We've essentially gone for a change in style (more wide players, no Drogba, lots of creative forward players, Torres etc..) but the midfield is one built for a different era.
On Chelsea forums, the transfer section has been about forwards and these creative players all summer. Now all of a sudden i'm seeing names like Modric come up again, Sahin, Witsel, Moutinho, Dembele, Martinez (before he signed for Bayern today). People are worried about it now, not sure what took them so long really!