The idea is not to take out the group of people. The idea is deterrence. These guys drew after the door was opened and forced their way in. The person robbed very well could have been CC'ing.
Now have the person OC'ing. OC'er answers the door, BG's see gun and promptly leave.
They leave because you have presented yourself as a hard target. They are looking for a soft target.
Thank you for your service as well.