It depends on the numbers. How many drones in the swarm? How many bitter clingers with shotguns in the counterswarm? Here’s where the consequences of gun rights show themselves with exceptional clarity. Gun rights and gun culture means lots of angry rednecks with shotguns. Lots and lots of them. Swarms of them.
Also, one side may be on death ground. That creates a psychological advantage. The other side will be complacent, or - with a Darth Vader type commander - even risk averse.
Also, the drones will be either remote controlled - reducing responsiveness quite a bit - or autonomous - lacking human ability to think outside the box. A well designed system will be a careful mix of the two, but a well designed system isn’t likely to happen.
It’s asymmetrical warfare. The phrase “an army of Davids” comes to mind.
Oh, and… eventually the defenders will have their own killbots. Crudely manufactured and few in number, but brilliantly designed. Because good engineers like freedom and thrive in freedom.
Oh, and of course they’ll hack the enemy’s control systems. Especially if they have a reason.