Even if he was the consensus 1st overall, that doesn't excuse the scouting department. Their job is not to follow the consensus: if it was, we wouldn't need them. They messed up by falling in love with what they wanted Slaf to be, which is something he isn't. He isn't a power forward, he isn't a beast in front of the net or in the corners, he's a playmaker who doesn't have the hockey IQ or processing speed to think the game quickly enough to make plays.
Maybe he can develop the reaction time or pattern recognition in the AHL, but right now he's trending to be somewhere between Bickell and Pouliot.