If we could just employ a high quality manager that makes their teams play good in attack we would be getting top 4 easily, it is the one type of manager we have yet to have employed since fergie left, Moyes was just not the type of manager that should be near a top 4 premier league club as shown with his downward spiral, same with Solskjear who is nowhere near a good manager, van Gaal and Mourinho are cautious managers that favour wingers that track back over wingers that can open a defence.
I think even if we had a manager like Emery we would be fine for top 4, considering what he had to do in the market with limitations over the past two seasons with arsenal I'm sure he could have done better job with the type of money afforded to Mourinho and van Gaal to spend on players.