Clubs usually look for managers with proven winning history to avoid risks and ensure good results. Ferguson huge success meant United trusted his judgment but if that trust led to decisions based on friendships over actual ability it certainly played big part in club decline.
It is clear that to succeed long term favoritism must be avoided in important choices like hiring manager. Even so your hope for Manchester United is valid. Many feel that with right choices and focus on merit club can definitely bounce back.
Maybe Manchester United made the right move with Ten Hag, because he achieved good results with Ajax, if you compare Liverpool's decision to take Slott as coach instead of Klopp, everything is similar, the only difference is that Slott came when Liverpool were doing well, and Ten Hag came during a big crisis. And after he left and with the arrival of Amorim, it is obvious that things got even worse, so you need to take everything into account before drawing conclusions, and at Bayer he can do much better.