The Manchester United team has only been built for a few seasons by Ten Hag and it is very different from Manchester City, I don't think it can be compared and in the future I still believe that if Ten Hag continues to make improvements and cover up the mistakes that have occurred then it is very likely that the Manchester team will United will be perfect again or match Manchester City's level for the title competition.
But, Ten Hag only have a year to build Manchester United, I don't think he can. If Manchester United didn't qualify for Champions League in the next season, I'm 100% believe they will sack Ten Hag ASAP. And then, the problem can't be resolved since the team always change the team for every one or two years.
The best solution is to sign Pep Guardiola or Ancelotti, because if they failed to bring Manchester United glory, the fans will blame the players instead of the managers, so they can survive and build Manchester United for many seasons.
I don't think Pep will ever coach United and same thing goes for Ancelotti who most likely will retire after Real Madrid or try his luck with a national team. For Pep is simple , United is stuck on old methods and doesn't want to carry a club who doesn't want to invest in modern training facilities and besides this , he is a City fan for real and he will not betray the fans to actually go and coach United.
Regarding Ten Hag , if the club still has trust in him , there must be a reason but if United won't deliver this new season , for sure he will leave the club and another coach will take it's place.