for this situation, I think we can compare Zinadine Zidane and Ryan Giggs. When Zidane manage Real Madrid, in the first year he get a champions league with that players. And now with manchester united play in under champions league competition called Europa League, with their squad now they can win the europa league with Ryan Giggs.
Ryan giggs should be much better coach compared with mourinho however Im pretty sure that the reason why manchester united doesnt give ryan giggs the chance to be the next coach is probably they dont want to sack ryan giggs incase he is doing bad so they still let him learn at this moment however mourinho definitely needs to be changed