The problems of Manchester United is inconsistency. The inconvenience might be attributed to unavailability of Manchester United players due to prolonged injuries. Erik Ten Hang has never had a handful of players available for him to choose. If defenders are available today, midfielders will not and if midfielders are available, strikers will be lacking. So, I applaud Erik Ten Hang for using an inconsistent team to go this far.
Manchester United might not be able to qualify for the top 4 this season but the management will have to buy new players for the next season in order to fight well.
But the problem that ten Hag didn't have that many players available as you are saying is not only because they were suffering from injuries all the time. One of the biggest reasons was that ten Hag scared away some of his players and made them leave the club again before they even arrived while others were ruled out by principle more or less. When ten Hag doesn't like a player, it is almost impossible for that player to ever get a fair chance to make it into the first eleven of the team. His approach sometimes seems to be too ideological in my opinion and he has an alpha male complex. He wants to have control and to prove to the whole world that he can discriminate against any player he wants because he is the boss. He is one of the worst coaches out there in my opinion.
With your all review about the Manchester United and Ten Hag I have understanding their biggest issue is not players or their performance their biggest issue is Ten Hag who completely fail to understand ground realities and also players physiology which is hurting this team badly in this season even mostly were expecting good performance from then.
If he fails to give something better before end of this season then most chances we will have him without job after the end of this season which is having not good memories for the fans and players as well change of coach surely can bring better results and improvement in performance like we have in Roma case which are now doing good after changing their coach which was doing nothing and creating mess-up which was hurting their performance and progress in their league.