Arsenal, Roma and Juventus are not better than Manchester United. If Manchester United can eliminate Barcelona their most deadly rivals, they can do that to any team. It is that simple. The winning mentality of Manchester United is so high for now. The new coach of the team carries pressure and the players are more United than before.
Do not underestimate Arsenal and Roma, they're a strong clubs without a crown. Juventus is a mediocre club, their performance isn't stable and they got beaten for 5 goals against Napoli, it's really a worst result for Juventus. Current Manchester United performance is really strong and they've beat Barcelona, but the goal difference is only a goal, Manchester United doesn't really humiliating Barcelona. So I believe Arsenal, Roma and Manchester United are equal clubs.
To be honest, I like Manchester United. at least, they offer us an interesting spectacle and the strength they have is when counterattacking. even so, it was not easy for The Red Devils to win this competition trophy. The reason is, they have a busy schedule of matches. The impact will gradually be seen. except, if United are still able to keep fit and stay primed.
after all, there are still other strong teams like Arsenal, who are ready to face whoever the opponent is. also, there are still Roma and Juventus that we cannot underestimate. although, the performance of these two teams was not at its best. but that does not mean, they will be easily defeated if they meet in the next round. Or, maybe Union Berlin will give us a surprise. I think the opportunity is still wide open for the team we mentioned here. but, yes, at least, The Red Devils are one of the strong candidates in this competition.