Indeed Manchester United have a good squad overall, but from some of the coaches who managed this team last season I would say they failed. I don't know what their failure was due to what factors, maybe from the players themselves or from the strategy the coach was given.
Not good enough. They only have above average squad that is in balance between defense and attacking. Their attacking is not bad but their defense is. Their attacking is not good enough to cover their defense so their general result is bad.
Every time a new coach manages this team it is always accompanied by the belief that they will be successful, but in reality they are not able to deliver everything that is expected. Now that Ten Hag came with the same expectation, the question was whether he would really be able to give his best or not.
Coaches are only parts of their issues, not their main or only issue. Issues are from their President, Woodward etc who had very bad strategy to develop the club. They spent a lot of money for transfers and salary but receive too little back. They failed to deal with other clubs and bought players at more expensive cost than other clubs would pay.
Many coaches had problems with transfers too. They were not given enough power to decide or reject what players they want or don't want to have in squad. Then they could not use those unwanted players well.