of course you can, but if your HC is the offensive genius that designs the whole offensive scheme, that that will stay the same for your young developing QB. If your OC is the one to design it then that only stays the same if your OC doesnt get plucked for a HC job.
its also about asset retention, If you have any success you're more likely to lose a great OC then a great DC, it took 33 years before Fangio got a shot as a HC.. compared to McDaniels, failed as a HC in Denver, got offered the HC job then fucked over the Colts and still got hired again as a HC for the Raiders.. Its an offensive League and great OCs get plucked for HC jobs...