> No matter how many guns you own, you can only shoot two at a time, and only one if you care about aim.

This is just as true for guns as drones. Both need fast reactions and fine control. A human cannot control a swarm of drones any better than they can control a swarm of guns, but you can add autonomy (sensors, actuators, compute) to either to get some of those capabilities back.

Conventional munitions will always be more economical. It's hard to beat a few grams of steel in price per kill. Drones are only relatively cheap when compared to rifles, but they're actually replacing bullets/bombs. Great for high value targets, less great for indiscriminate killing.