While the leagues are of course vastly different, Lyon is doing a bit better if I am not wrong. They have 45 points in 26 games, which is about 1.73 points per game, and fifth place at Ligue 1 as well. Whereas United has 37 points in 29 games, which is about 1.27 points per game, and they are 13th in the league. I am not comparing ligue 1 with premier league, of course premier league is harder to do better but that doesn't mean these two teams are close to each other normally.
Just because United is United, people see a chance for them to win, after all they got here so far, so they have a chance to move further too. But I would say if we were to compare seasons, Lyon has been better this season overall than United.
In terms of the achievement of each league's standings, it may be true that Lyon is much better than Manchester United, but we also have to look at the competition between the two leagues which is different because the Premier League is much more difficult than Ligue 1. Manchester United is used to facing pressure in the Premier League so it is a little easier to face pressure when facing Lyon.
But this is not a guarantee because the match is not determined by how good each League is. Both have a chance to qualify as long as they take advantage of each team's weaknesses and in terms of pressure, Manchester United may be much more prepared.