Di Maria does dictate their tempo of play, but the same can be said for ourselves, with how much we rely on Sturridge. You can't exactly argue that they have the case of relying on one player, when we are the same.
Their defence is a mess, but we can hardly preach. Our backline is a shambles in itself. Just like them, we also lack the ability to control and dominate through the middle but the edge they have is that they have more goals and creativity coming through the likes of Di Maria and Herrera. We can't say the same for Henderson and Allen.
I think both of us have very similar issues in the back and the middle of the park - being soft centred and possessing the ability to dominate a game, but frankly they have the edge in goal production from their centre midfield and attack.
That'll be the difference between both of us in the end.
Strikers don't dictate the tempo, midfielders do. We aren't missing Sturridge for his passes, but for his movement into space and most importantly for his finishing. And either way you turn it: you can't just ignore certain aspects of a midfield. United do have a great attacking midfield with Di Maria, Mata and Herrera (& Rooney sometimes), admittedly better (on paper) than Sterling, Coutinho and Lallana. The defensive midfield is way more important for any team though, because you dictate the play with your defensive midfield. Just compare Gerrard, Lucas, Henderson, Allen and Can to Fletcher, Carrick, Blind, Fellaini and Herrera (who isn't really a defensive midfielder, but gets played there nonetheless). That's why United failed so miserably to close the game off when being up 3-1. They couldn't dictate play and they most certainly couldn't just hold the ball. You're right in your assessment that Di Maria and Herrera will create more than Henderson and Allen. Consequently, they will also be responsibly for more goals conceded. And Henderson and Allen can actually tackle, win and keep the ball.
And seriously, you can't compare our defenses and say we have similar problems. Even our 4th choice central defender (Toure) would play every week for United. We have two proven PL players with Skrtel and Lovren, Sakho who can do a great job but lacks consistency and Toure, an experienced and proven PL CB. United have Evans, Smalling, Jones and Blackett as their CB core. 4 homegrown players who consistently underachieve (or simply are shit) or play their first PL season. Our fullbacks are certainly better too with Moreno, Enrique and Johnson, Flanagan, Manquillo. Compared to Rafael, Shaw, Rojo and whoever they might have on their books. Just compare the individual quality (=on paper quality) of those players like you did with the attacking department. It is blatantly obvious that LFC has the better players.
They might have the better attack, that's something that first has to be proven though. Under Rodgers we have never had a problem of scoring goals after he had settled in for a few months. Van Gaal has yet to prove that his team can score goals against decent sides before anyone can say their attack is better than ours. We certainly have the better defense and defensive midfield though, you can't even argue about it because it is so blatant. Or let's just say it this way: our team is much better balanced and that's why we will finish above them.