What you say about helicopters not being able to change speed on the rotor and requiring blade pitch is true, but at the size of helicopters, it has far less to

What you say about helicopters not being able to change speed on the rotor and requiring blade pitch is true, but at the size of helicopters, it has far less to do with the speed at which the engine can change RPMs as just pure inertia of the giant helicopter blade. I am a helicopter pilot, and I can generally adjust the speed of the engine much more rapidly than the rotor speed itself adjusts. I suspect that's a large part of the reason for the multiple rotors on this drone. If they get larger, you're no longer able to rapidly adjust the speed of it just from pure inertia.