Manchester United's job is easier now after Arsenal have been eliminated in the Europa League. But by saying easier I don't mean they will be very comfortable. There are still challenging teams in the tournament now. Besides if they get past Sevilla their opponent will be one of Sporting and Juventus. I assume it would be Juventus if they play carefully against Sporting.
Manchester United should be able to eliminate this Sevilla as well. Sevilla are far away from even their performance in the previous season.
Indeed, it seems that Manchester United's journey in the European League has been fairly smooth and since the preliminary round they have always been met by a team from Spain. Sevilla is the third team from Spain that will face Manchester United in the quarter-finals, previously Manchester United successfully brought Barcelona and Real Betis home first. If Manchester United manages to get rid of Sevilla, I think their next opponent will be Sporting because they have more difficult matches to get to this round and I think it's really worth it if the opponent is Manchester United.