If we get about what we have now next season that's treading water. We didn't accept it from Moyes when he was nailing that average for a few years on a lot less cash than this feller is spending, so why should he get a free pass?
I don't see moving up the league as treading water. As I said, 7th/8th this year then 6th next year is improvement.
If we managed to catch up and get 6th this year, then yeah, I'd be looking at CL / 5th next season as being improvement.
That said I'm keen to move forwards as quickly as you are, but if Koeman improves our league position in his first 2 seasons, I'd find it difficult to say he's not performed.