I don't think it is is many United fan; frankly, the way the club have been going, a lot of us ( including myself), at this stage, would happy with above average. Look at the love Bruno ( and to a lesser degree Rashford) get despite having plenty of flaws ( esp. when compared to the greats of United past).
Fergie got a lot more conservative in terms of attacking football later on in his career, so you could argue that he would also have gone more possession- oriented, but he still tried to turn Anderson ( a CAM) into a deep lying midfielder. He still romantically played 2 in the middle ( Carrick plus giggs) in the CL final against Barca ( even though Chelsea had shown the way to beat them would be to muck it up). I, still, remember his playing Berbatov and Carrick as CB in a league/FA Cup match. So I could argue that him being conservative at the end might have been the function of the Glazernomics rather than him just being more conservative ( plus quieroz).
In terms of why the top managers are possession based managers, it could be because the executives in the big box are risk averse and copy what is working instead of trying to be innovative. Jerry west, a great NBA executive, mentioned that a lot of executives were more interested in keeping their job than winning; this means if ETH fails, the guy in charge can say oh we tried Pep Regen, but if they get a manager who plays completely differently ( and he fails), the executives will be likely mocked and fired.