The answer to your question lies in this line
"they have been wank at United"
I wonder why? Coincedence?
Mourinho got money to spend at first to get CL and spent it well. We improved a lot from Van Gaal. We finished 2nd to City who spent double what we did in the time Guardiola and Mourinho took over and with Guardiola taking over a better squad containing Kompany, Silva, Fernandinho, Aguero, De Bruyne, Sterling. Finishing 2nd to that is not under achieving.
And when he needed further backing to help close the gap?
Nothing doing. Because the owners are happy with where we are at.
The result is that the manager of our football club is under huge pressure to deliver at the top of the football pyramid without ever really having the right backing either through competency of the board or consistent, note the word consistent, spending on players.
The next manager, whoever your choice would be, will find himself "wank at United" too I'd suggest.
Without counting Sanchez the club spent 400m since Mourinho took over, there has been consistency. The manager has consistently purchased players that he fails to integrate in a cohesive team. Maybe you think that 600m-700m should have been spent, I don't.