Willian is fine as our 3rd AM. With Fabregas in the DP we'll never be able to play with classic roles anyway, so as long as Willian helps Matic defending for Fabregas while keeping possession when we're attacking Willian's alright. We could do better but as of right now, he's one of our least problems.
He'll take us one step forward so it's okay; I just hope this transfer doesn't mean that we won't be going for a 3 steps-type attacking midfielder next summer.
I don't think benching Asmir for Courtois should be a move that Mou should do. It would send just about the worst signal to the team and any future signing.