I'm sure it's been touched on but playing the 4-3-3 this way in midfield is something from a Tony Pulis manual. The idea of dropping that flat three in there instead of keeping one guy up as per the 4-2-3-1 is to mitigate risk, so you're actually freed tactically such that you've two players now making runs from deep, linking up who are essentially converted creative attackers, while one holds. Bundling the likes of Hendo - Can - Gini (who should be from the converted creative attacker school but simply doesn't exist) - Milner etc together is the kind of shctick we give Pulis for playing a line of 4 centrebacks.
You look at a side like Napoli for example, who use 4-3-3 as well, and look at the profile of their midfield. Obviously the return of Lallana and a signing in place of Coutinho will help, but even in their absence, you don't need to go all caveman. It really isn't that hard playing as part of a flat 3, that's the point really, get more creative attackers in there if we're going to persist with it in the season. Otherwise the 4-2-3-1 fits some of our strikers quite nicely.