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.
I think what is bringing this comparison was Manchester United's recent match against Leicester City which they succeeded winning. This is not enough for Manchester United to stand against Chelsea. I think this person is making a huge mistake or maybe is just trying to tell a story which is not true, Manchester United are not anywhere closer to Chelsea despite they are not in the best form. Just imagine a team that is fighting for a slot in top four and a team that is struggling to even make it to top 10 at the end of the season, I don't think there's anything to compare here. The margin is clear Manchester United should just come back next season stronger but this season they should just forget about being in the same level with Chelsea. Chelsea has gone far and with the rate of their performance now I expect them to come back next season stronger.
Europa league is not even clear for them to win it but they are having a wonderful performance in the competition, I have hope for them in willing the title. But let see how it will end.