Miller is the 7th best D, but he's a right-shot and Cassidy favorite.
He's usually fairly solid for a few games, then tosses up a stinker where you just shake your head at some of his decisions. Last night was one of the those games. Last Saturday in Toronto was another. The Bruins shut-out the Leafs if not for Miller. In the span of two shifts he was the main cause of two goals against. First goal he couldn't make a simple break out pass and made an egregious turnover and the Leafs kept the puck in a scored. Next shift he took a penalty and they scored on the PP.
People get all giddy with his hits but that's not the be-all end-all. He's a better fighter than he gets credit for.
That's not to say he's a bad D-man, or that he needs to go, but I see no reason for him to be immune to sitting out a game at time like Moore and Gryz have done.