Arteta is very good at some things as a manager, if he wasn't we wouldn't have been in the title race at all. I don't think we'll be worse next season, although the CL may stretch us a bit. I do think Arteta is going to have to learn fast from this season though. I reckon there'll be a lot of optimism going into next season but it'll come with a lot more expectation than this season. I just think theres a bit of a magic trick Arteta is doing in terms of motivation and belief that wont last if we don't manage to sustain our level in the league and push a bit harder in other competitions.
I don't think being 2nd and having no cup runs is over achieving after 3 and a half years though. Its a solid job but my expectations when a new manager comes in would always be that we should be here or better after that amount of time. Especially given the unprecedented spending in that time.