I think it is hard to judge TBH, all of the managers we have had post Fergie have been significantly hampered by players that they didn't want either being bought in or given ludicrous contracts so it has been impossible for them to fulfil their potential, woody said as much in his statement, they did not do well by the post SAF managers, in particular we have been screaming out for a decent defensive midfielder since Keane left, we had enough with Carrick and Fletcher to cope for a while but since it has been a mess.
Given more time and freedom would Moyes have succeeded?
Without poor signings, Di Maria and Sancho would Van Gaal have brought in more suitable players?
Without the scourge that is Pogba, and if he had been allowed to sign Maquire would Mourinho still be here?
Without Ronaldo unsettling things, and the unnecessary addition of Sancho would Solskjaer still have the job?
In fairness I would say out of all of the managers we have had since SAF I have enjoyed (for the main part) the time under Solskjaer the most, the style of play and jettisoning of players, and surely that is what it comes down to how much you enjoy watching your team, you can say Mourinho won a trophy, but really was it fun to watch? Van Gaal got us keeping 80+ % possession but I was interminably dull, Moyes is the unknown for me he lost the dressing room and that was it, if he had come in later not straight after SAF I think it would have been different for him, not saying he would have done better just that it is very hard to judge Moyes he was a sacrificial lamb.
I think also in fairness to Solskjaer it has to be said that Rangnick is still experiencing the same difficulties that he did, I think the club had no options but to ditch Solskjaer but that clearly hasn't resolved things, I also think that Solskjaer exceeded his capabilities and that we needed to move on so not bemoaning his sacking.
We have said many times there is a lot more needs fixing at Utd than the manager and the odd player.