Expanding on your point #1: The inertia of large props means they can't change speed quickly, so there will be lag in the control inputs. (In toy quadcopters,

Expanding on your point #1: The inertia of large props means they can't change speed quickly, so there will be lag in the control inputs. (In toy quadcopters, electric motor torque is so high vs prop inertia that lag is a non-issue.) Collective pitch controls don't exhibit this lag. Electronic controls can compensate for inertia lag to some extent, but they have to be carefully designed using control theory, and if they fail the copter will likely be uncontrollable.