Most of the small high speed drones are that size to fit under professional licencing requirements, often so that one racing spec can be viable across a wider area. Leading to significant competition in that size pushing down prices.

Rather than some inherent sized for safety idea.

Jamming might be interesting, I suspect that it's easy enough (and a much bigger crime) to follow a very loud jamming signal though.

Every practical metric a drone surpasses a helicopter; they are so much simpler to operate that you can easily offset any perceived downside with more drones. And you don't get a tested solution without trying it out.