I don't think with Arsenal and Barcelona only are the team have favorite for Europe League winner because still have Juventus back to consistency performance at last six matches, right now Europe League tittle race most competitive for winning the second competition level on European. Honestly, Arsenal have better quite appearance in this season at domestic league and European League but I doubt can consistency because next round of European League begin on February next years.
Many predicting the winner of European League between Barcelona and Arsenal but the problem right now Barcelona have against with United on play off round.
I don't think so either because apart from Arsenal and Barcelona there are also other top opponents in the Europa league this season who are capable of winning, teams like Juventus and even Manchester United will definitely be tough contenders for the trophy but as an Arsenal fan I will be supporting my team to win it in the end which I guess should be understandable lol.
You cannot be counting Barcelona as favourites to win the Europa League when they have not overcome Manchester United that is a big challenge for them. If you want to count favourites, it will.be fine you mention both of them because anyone that won between Manchester United and Barcelona may likely get to the finals of the Europa League for this season. It is unfortunate that the two big teams met early