I have questioned Troy as a coach for a while now. Obviously the fact that Thornton is brittle cannot be coached up (other than teaching him to protect himself from injuries as best as possible, but I don't think that is why Thornton has been constantly injured), but I still think most of his biggest issues (route running, running through routes, managing the sidelines) are all coachable things.
Douglas is not the best route runner either and runs a lot of of the wrong routes, but that can be hid because he is a player you get the ball to quickly and he can improvise after that.
When Troy said last year that he didn't think the fact the receiver were all bunched together on their routes wasn't an issue, I really started to question his coaching.