No matter who the manager is, you need to have a quality squad to compete and we just dont have that.
One can look at the quality and quantity of players other teams have brought in, and United simply cant compare. These same teams had better squads back then but continue to improve while united squad is deteriorating. We still have Fellani, Smalling, Valencia, Young etc starting
Outside of Pogba, other recent signings are either past their peak (Sanchez and Matic) or just average to good. United need to overhaul the squad and inject young and top quality talent. Two decades ago, the likes of Kane would already be in red
Of course, Mou has made it worse with his usual childish tantrum he throws when he doesnt get his way. On the field he is trying to compensate for lack of defensive quality with numbers but that never truly works. But to sack him when you have not really given him much to work with is not going to magically fix anything.
Modern day football is not a profit making business. To win immediately you need to invest astronomical amounts, otherwise you do a very slow build up and hope you can spot top talents early enough and hold on to them long enough. United need to improve massively in both scouting and in transfer dealing.