I think if a new coach joins and starts building from now it will be better. Manchester United are out of the Champions League, and they are in 7th position in the Premier League. I don't think they can achieve anything this season. The maximum that they can achieve is to book themselves a spot in the Europa League for next season if they continue under Ten Hag. A new coach can also join and would probably have the same result. If they start building the team from now, it will be better and they can deliver it better from the start of next season.
Manchester United are 6 points off the Top four with 21 games left to play, so I wouldn’t rule them out just yet, they can simply get there season back and still qualify but not with the current form, so things have to definitely change. I see your suggestion is a changing the manager which is common in football when a team is facing problems, but I will disagree with this one. Manchester United have changed manager since Sir Alex left the club for almost five times now and are still struggling. The first season the coach arrives he performs and gives the fans hope and the next season the manager gets a bad season. I have analyzed this case and I will say it is mostly the board problem, the second season is meant for you to back your manager with signings but they don’t and instead sign players that suit them and not the managers pattern and that causes the manager to twerk his style of play and it affects the team.
I would say united need to keep Ten Hag even if it’s for at least a season and then sign his players and also get rid of those players that have been in the club for too long. A total rebuild must happen before the manger is talked about this time around