He's clearly a decent shot stopper. It's perfectly possible the coaching team can improve his distribution and positioning, particularly if he gets a bit more gametime which he will this season. I'm still worried about him tbh, but other players have improved under Emery and I'm prepared to be proven wrong about Olsen.
If he's making these mistakes in matches, he's making them in training. Emery and his coaching staff must feel that they can improve his distribution in time. It's painful to watch but if Emery sees his as our number 2, there must be a reason. I think Emery's quite able to be ruthless when he needs to.