He isn't a top gm either. But he's far from a bottom 5 GM. He's very average. Some good moves. Some bad moves. But so far, no terrible moves that have put the franchise in a huge bind (like signing Xander Bogaerts to 11 years and 280 million).
The big moves he has made (Olson and Murphy) have mostly worked out ok, though we would be better off if those moves weren't made (assuming we re-signed Freeman in the Olson case). I would say the biggest issue is the super lackluster trade deadline activity every year and the previous 2 off-seasons being very bland.
That being said, if he was fired tomorrow, I wouldn't cry about it.