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.
I agree here. I think that Manchester United is at least on the same level as Arsenal, AS Roma. In my opinion Juventus usually is still a little better than Manchester United but at the moment ManU seems to be in a really good shape and they are also having the momentum on their side, so if the match between ManU and Juve would happen today it would also be a completely open game to me.
I also think though we should not forget about some underdogs here that could create a major upset like Eintracht Frankfurt managed to do in the last season, when they have won the cup.
Union Berlin for example eliminated Ajax Amsterdam in a pretty impressive way.