Let's wait for unusual performances in the Europa League this season from those on the list of clubs participating in the Europa League. For some clubs they have to play a play off match first, and for some others they have been waiting for their next opponent in the knockout phase. Clubs that are now seeded are also seeded in domestic leagues such as Arsenal and Barcelona. I agree they will put their domestic league first and after that they will put the Europa League. No wonder because many see that the Europa League is not more prestigious than their respective leagues.
Still not excited yet with Europe League right now because waiting with play off match result and several team qualify to next round trough first standing position finished waiting their opponent after play off match result. Loss bigger team early between Manchester United or Barcelona after both team face on play off round, I think Manchester United vs Barcelona happening at semifinal or final stage but failure finish on first standing make United have been in play off round before qualifying to next round.
Arsenal have consistency performance on domestic league in this season and have favorite lead to final in Europe League, still don't know about who opponent team for Arsenal on next round and I won't if big match happen on early stage.