I totally agree with you, the team isn't doing well in the league but they have somehow managed to keep a incredible record in the Europa league so far this season. Personally, I don't think the coach is a problem but it's the club that's the main problem to the club itself. With the way things are going for Manchester United I really don't think they will get their Spanish opponent in the Europa league Round of 16.
I see it realistically and not excessively because so far Manchester United has not met a strong opponent in the Europa League so they have not found any difficulties and for the future I think it will not be easy for Manchester United, especially if they meet a tough opponent and what must be remembered is that the competition in the Europa League is very fierce so I will not put high hopes or expectations on Manchester United this season, they are really very bad in terms of strength and consistency so I do not expect any surprises that they will do in the Europa League.
I'm definitely not going to have high hopes on Manchester United, just like you said, so far they haven't yet met a tough opponent in the competition so far that's why it seems as if they haven't lost a single game. Once they meet a worthy opponent, I think they will definitely snap thereby crashing out of the competition sooner or later. After this round of 16, it will come to the point where only the consistent team is left to battle it out.