La Liga also won't be easier for Sevilla although that is important to consider because La Liga is its own domestic league. Next season Sevilla will no longer be in the Europa League which of course has to focus more on the Champions League because Sevilla has won the Europa League and that will of course be even tougher for Sevilla because the Champions League is a collection of the best teams in all leagues.
Of course football will always be tough that's not an excuse to remain the same, let the victory of Sevilla in the Europa League be a starting point for them to do better against the Champions League next season and also in La Liga because right now I think they a big team when it comes to Europa, they should be able to strive for something bigger.