As I said in the article, I don't think Leslie had a bad year. Far from it. He just didn't have a great year. When you send a player back for his overage season, there are generally pretty big expectations for their play and progression. Just look at what Colin Miller was able to accomplish in his overage year.
He's still a solid prospect, but I'm a bit worried he could be a bit of a tweener. As you said, he's a smart defender at both ends, but if often takes more than that. Being a pretty good offensive defender, and a pretty good defensive defender, but not outstanding at either can be a kiss of death for a defensive prospect. In that same regard, he could be compared to a guy like David Kolomatis, who definitely developed into a quality AHL defender, but whose lack of a particularly dominant trait kept him from the NHL.
We'll see how he develops as a pro though.