I have no doubts he'll improve on what Ancelotti did last season (nothing, basically)
He finished 10th, and I could see Rafa getting them 8th. They also had a poor window with no significant buys, but if he can keep Townsend and Gray producing every once in a while, they'll be seen as good signings.
In the long term, it might not be too bad if they have an alright season this year. By alright I mean finishing just outside of a European place. The worst thing they can do from here is start rewarding players in their late 20s long term deals, the likes of Michael Keane and Allan, etc. When it eventually does go wrong, the next man will be taking over a squad worse than they had when Marco Silva came in.