While everybody appreciates his consistent hard work and tracking back, as you mention in your post, he has a shocking lack of impact far too often in the final third of the pitch, reflected, again as you show, in his numbers. At least from me, that's what I mean from "goes missing", i.e. "goes missing where it counts".
I remember that time he turned that Leicester defender inside out two years ago to set up a goal for us, and literally cannot remember another time where he's waltzed past somebody and turned that into something meaningful.
Like I said, if he were on much lower wages I'd be all for keeping him, but I don't think Everton can have somebody on 150k a week who doesn't produce week-in, week-out. I think it's a huge shame as I really, really appreciate what he can do as a footballer.
That said, if somehow Everton find it financially alright to have 150k-a-week attacking midfielders who score two goals a season, then I would definitely champion keeping him as he does bring the best out of other players, when he is on form.