True, Ghorn will outdo DB for raw damage. But a utility use, such as keeping a zone clear, can sometimes be much more useful than just dealing damage. Take his Thrall example on CE. Keep them away entirely for a few seconds, versus nuking a large handful that immediately get replaced with another swarm, barely giving you a second to breathe. Sure, you killed more with Ghorn, but it didn't give you as much room to recover as DB does. DB is better in that sort of situation.