Exactly, the defensive lineman must be disciplined and stay in their rush lanes and not let the QB break containment. It's not as much about getting to QB as it is keeping him in the pocket. Mr Slimm, why do think some Dlineman having such a hard time grasping this concept. Example, 3rd and 15. Vick is in the shotgun facing 4 down lineman. Both DE's blast up the field like their rears are on fire and Vick slips out the back door for a big gain. I just sit and shake my head.
This, though, severely limits the pass rush. If the dual threat is competent, it makes life relatively easy.