If they can take corrections from the mistake they made this season and making improvements of their performance they fit be the best team next coming season that means if they make a concrete arrangement. Because this season didn't fevor Manchester United and the Chelsea at all is like the Chelsea performance was even get better than the Man united even though they where also not good though the season they perform admirable against some of their opponents.
In fact, the performance of these two teams was very complex and at the end of the season both of them were pushing each other to finish in a better place. I think Chelsea beat Manchester United yesterday by finishing above them and securing a place in the conference league, but what we saw from Manchester United after winning the FA Cup made them get a place in the European league.
It is clear that in the end Manchester United could reverse Chelsea's previous situation and even though they finished below Chelsea, they won the title and also had slightly better European competition. I think both teams should recover next season and regarding the polemic about changing coaches between the two, it will definitely take a long time to build everything from scratch.
Considering how Manchester United and Chelsea started the season, I didn't even know they would each have a slot in the European competitions at last but since they managed to make improvements towards the ending part of the league, if they continue same way next season then they would do better in the European competitions. Whether Manchester United have a more better European league than Chelsea that is not important, they most important thing is for each one of them to come out stronger and play better than they did this just concluded season.
Literally, if a new coach is appointed to take over managerial duty of these two teams it will take time before the coaches will understand the football ethics of the both clubs but however, even if it will take a new coach a whole lot of time to rebuild the team i think that will be better instead of them to just continue lacking improvements year in year out.