Needless to say, there's a lot of details like the ones you're discussing that can be put together from open source -just like you have here. But there's a lot of not-open-source details included in what we are being briefed, talking about, chewing on, and developing TTP's around.
Short version is that good semiauto scatter guns with red dots give you a sliver of a chance against drones, which is better than no chance at all.
It's also immediately available and relatively easy to field, the only issues are the doctrinal resistance, the harrumphing old coots with a eagles and stars on their chest that hate the idea of giving Soldiers any kind of actual weapon, and of course developing a weapon qual for an anti-drone shotgun.
Naturally, the industry is hyperactively pursuing kinetic and non-kinetic drone defense systems and salivating at the possible profits.
Putting it in P-F terms, Shotguns vs Drones is basically being the dude with a pocketed J-frame and a mouthful of burrito when three dudes with AK's roll into the food court and start shooting. Meaning, you don't have a good chance, but a slim chance is better than no chance at all.