The level of competition in the premier League is not better than the rest of European leagues competition what happen last season was that Manchester United was only desperate and needed to win the Europa League so that they can play in the champions League that was why they were so putting all efforts to make sure that they win the league, they where very poor in the Europa League group stages as they were drawing games
You cannot compare the competition level of the EPL to playing in the Europa League in anyway, the number of games each club has to play per season is almost three times the number of games played in a single Europa league competition. Manchester United were already too far behind in the league with few games left to make a difference so they turned all focus to the Europa League with fewer games and a better chance to win something but thank God they failed, the world is a peaceful place because they didn’t win.