Obviously Chelsea is better than United, they are not even remotely close to each other this season, Chelsea is fighting to be third place, and at worst be in UCL at least. They will probably win the conference league, so they do not need to go to Europa league from the league stage, they can do that with conference league, they need to go to UCL and the path for that lays with fourth place.
By comparison, United is doubtful about being 10th place, not only United will not be in any European competition next year (unless they win Europa league and I doubt that) because they will be outside of top 10, that should be the main reason why they have such a gap between these two clubs, we are not going to see them do any better.
Unless Nottingham Forest fall out of place, I will continue to give that credit of bouce back to Manchester City that they are going to come back to the top 4 before the season ends, Chelsea are not far away from Manchester City and as long as they keep losing, it doesn't matter if they are better than Manchester United or not, they might not get the chance to return to the Champions League by next season except if Nottingham Forest don't make it again.
I don't like the basis on which Manchester United starred this season. Chelsea has repeatedly did this in the past by changing coach and expected to see good result but nothing really changes, they finally wait and bring in a new coach to have a fresh start with the boys before they came to where they are right now. I'm afraid to say that Manchester united struggle might not end in the season, even by next season it's going to be struggle upon struggle, Amorim can't change this club.