Before this year Andrew Miller wasn't a guy you even dared give the ball. Year by year his season lines were beyond wretched. He's only had one year in the past where he was even halfway tolerable and he was completely dead in the water last year.
As bad as he's looked recently, this is still progress for him. I wouldn't call him a good pitcher, but he's at a level where he's mixing some tolerable to decent starts in, and you can ask the question -- well, what do you expect out of a guy who's 7th in the starter depth? He's a bad major leaguer but a major leaguer.
I hope the Red Sox work with Miller for maybe another year or two. I don't think he'll be an ace at any point, but he's drifting gradually in the general direction of adequacy, and as a depth option, he's a guy you could get lucky on for a few starts to replace an injury, which is all you need to get out of the guy for what we're paying him. It is frustrating though, because even where he sucks you can see how he could be overpowering if he could just find the freaking zone. But he's what he is, and we can still get use out of him.