It's hard to prove that JM hasn't wanted his signings. I think that it's true that at certain clubs the chairman and board decide who they are going to buy and the manager basically has to fit them into the squad, regardless of whether he wanted them or not. I have read that that has happened at both Chelsea and Real Madrid in the past, but I've never seen anything to indicate that's the case at United. I think if Jose has said that then most likely he's making excuses for why the players aren't playing well. Most of this season he's given the impression of someone covering his own backside, blaming everyone but himself for the failings at United. Sure, there is some blame that needs to be laid at the doorstep of Woodward and the board, but a huge chunk of it needs to be assigned to Mourinho himself.
Mourinho seems like a complete dinosaur now, totally out of touch with football. Managers such as Klopp, Pep, Poch, Eddie Howe, etc have shown that there is a particular style of football and man management that breeds success. They all treat their squad like family and seem to genuinely care about each individual. They take the blame if things aren't going well and shield their players from any criticism, and in particular they avoid criticising their players in public. Ferguson used to be brilliant at doing that as well. Mourinho, on the other hand, seems to constantly publicly criticise his players. I'm not sure whether he thinks this will motivate them or whether he is simply trying to protect his reputation and legacy as a manager. I genuinely think he thinks he can do no wrong.
The other issue JM has is that he plays such boring, negative football that as soon as the results go bad, people turn against him. With the managers I mentioned above you'd be confident that any blip in form would be rectifiable. They all play good football and I think they'd all be confident that sticking to their footballing principles would see them through any bad runs of form. As fez has said, it's not the poor results that United fans are tired of, it's that coupled with watching boring football. We haven't seen consistently exciting football from United since Ferguson retired, which is five years ago now. I think Mourinho being sacked at some point is the only realistic outcome at this stage, I simply can't see him turning it around.