Next season it is still very possible to expect more surprises in the Europa League because besides there are many big teams who will compete there, of course there are many other teams who are not favorites to win the title but those teams can beat big teams like what happened last season when Liverpool lost in the Europa League. And usually teams like Sevilla or others who are not too focused on the domestic league will put their focus more on the Europa League for a trophy, but as you said in the Europa League next season nothing is easy to achieve for any team except for the team that really has great ability.
The Liverpool incident last season has turned out an eye opener to many others that winning the Europa is something any team other than the bigger teams can do, interestingly this is one of the rare occasions as Atlanta isn't a regular winner of the Europa, they even made a record amongst their Italian mates winning the Europa last season. Sevilla didn't qualify for the Europa so I think there's a mix-up with your reference. Although Sevilla happens to have the most Europa trophy and if they were to be in the league this season with their experience I believe the would have been able to do something interesting.
A team must really be able to maintain its best form in every match to lead them to become champions. Last season Atalanta managed to do that because they were able to maintain their best quality when they faced the favorite team.
For this season, the competition will of course be more aggressive in achieving their goal of becoming champions. This season there are even many big teams competing in the European league and seeing that their strengths are almost the same will of course make the competition even fiercer.
Roma, who have always failed to become champions, will again show their ambition to do better this season. De Rossi must be able to bring Roma to become champions because Roma is a team full of experience in the European league.