I mean I love my little racing quad just as much as anyone, but it's not like the three (or 5.. i also have a hexa) extra props/motors increase the dependability of the device. Lose one of those and it's a shitshow headed into the ground.
Of course, this reasoning doesn't usually account for the cost of implementing all that safety and redundancy stuff that was previously just understood to be possible. Not to mention the cost of getting it FAA-certified when you're done.
Maybe they're onto something.
A helicopter can land with the engine out by using it's rotors like a wing essentially. If these rotors are fixed, then essentially it becomes a falling brick.
On the Volocopter, the 18 rotors are fixed pitch, but yeah, a couple of engine/rotor failures are no big deal. Beyond that, ballistic rescue parachute: autorotation is not an option.
I suspect that there can be a way to relatively passively control auto-rotation of drone-style rotors. Pitch control is much trickier. It's not unheard of (even model planes sometimes have variable-pitch propellers), but it would noticeably complicate the rotor, lowering its reliability. I suspect that a fixed-pitch rotor with an independent mechanical axis brake could be much more reliable with comparable efficiency.
It's like a wing in the sense that it resembles the operation of an autogyro, which has an unpowered rotary wing.
In any case, the controller is probably going to be the bigger reliability factor here, and having more rotors doesn't help with that.