I wouldn't say a very good GM. Maybe just a good GM in him. He does have some upside. Building from the farm. Aquiring underated/undervalued/'problem' players. I don't think he understands advanced stats and such and it prevents him from having the ability to be a very good GM until he opens his mind to them.
But it does look like he was pushed into the situation we're in now. The worst part about this is the things that he does well, he can't do them now. He's being forced to trade his prospects to fit the window and he may not be able to acquire a Morrow type player because Beeston is looking for vets and proven players. AA probably isn't even allowed to trade guys like Janssen because we're trying to compete now, when he should be capitalizing on their value, all because the people above him want to win now.