I've pointed this out before.
Anyone who thinks Roof can't coach is suffering from a basic error. Roof, just like all coaches in college football, knows what needs to be done. The problem has been our lack of D talent to do it, especially at DT. Cerg, Glanton, and Adams are all big enough, but the last two are still young and none of them - unfortunately - has shown the physical talent to take over yet. That could still happen, but we need to get lucky. The rest of the D is ok; not great, but ok. Luckily, we have more talented players in the pipe that could make a difference going forward. Give Roof the talent - in this case, the size and talent - and he'll produce; he already has.
Our D recruiting for the last two years has picked up, so we might solve this problem going forward. We have to be aware of how much sheer bum luck is involved in finding great DLs, however. Nobody much recruited Aaron McDonald; too short and too small, everyone - but Pitt - said. Randy White was recruited as an LB; it took Bobby a week to move him to DT. Warren Sapp was not seen as a prime recruit for da U until his first few practices, much to The Rock's chagrin. And nobody but Bobby would touch Marco Coleman; he was a "tween" (too small to be a DL, to slow to be an LB) for everyone else. I hope we get this lucky again.