Wait... so we ended up improving our finishing position in both seasons we were in the Europa League in the past 10 years. Go Europa!
It looks like in general, that it doesn't affect the better teams like us, City, Everton, Spurs, and it massively affects the teams that are in on a once off like Newcastle and Portsmouth. It's probably arguable that those teams were on a good streak the season before anyway, and would probably have done worse with or without Europe.
I'd prefer us to be in Europe, and to win as many games as possible. If we do well in Europe, I think we'll do well in the league too.