Gun drones are perfectly viable. They just can’t fire well while flying. (At least not more than 1 shot) The current prototypes have to land and anchor themselves. They are currently machine guns, for area suppression, though anti-material would be viable.

The gun drone is also not in the smoke cloud, it’s behind it. The smoke, chaff, strobes etc are just to break the ability to counter target it. You don’t need to just saturate the cloud, but the whole area behind it.

As for the smoke, it’s not 1 cloud. A drone’s advantage is hyper mobility. A swarm would easily attack from multiple directions. Your gun is now required to saturate multiple clouds at multiple angles. 1 might be hiding something nasty, or 2 or none. Smoke (or chaff etc) drones would be dirt cheap, as would simple distraction drones.

To fight it, you would either need to put up a wall of shrapnel, which would quickly deplete a mobile weapon, or get accurate targeting data. Both could be viable, depending on the situation, but it’s risky.

As for engagement ranges. A drone swarm would be cut down by advancing over a large open area. I fully agree on that. It would also struggle engaging fixed defences. That changes in a city, or forest, or mountainous area. A patrol or convoy could be encircled by a swarm in seconds, engaging from multiple sides simultaneously.

Your gun can fire 10 rounds a second. That’s 50 rounds in 5 seconds. 200 micro drones, hitting from all sides could easily overwhelm it. Most don’t even need a payload, they are $10-20 decoys. 1 clean hit on your gun however, and it is potentially disabled. At that point the more expensive stuff can potentially attack with impunity.