Yeah. Quadcopters are far less efficient than single-rotor aircraft, and multicopters (hexa, octa) are even less efficient.
The reason people go to hexas and octas is that scaling a quadcopter up to the payload sizes of some of the octas/hexas starts causing issues with blade inertia - an octacopter is more stable.
The main reason quadcopters are doing so well for small aircraft is that at that size class, the mechanical complexity (tail rotor with transmission and collective pitch, plus collective and cyclic pitch control for the main rotor) of a single rotor or dual-rotor aircraft adds a LOT of cost. (The only flight controls of quadcopters are motor speed, with a few exceptions of quads with collective pitch which is still FAR simpler than cyclic pitch control) Once you get to a fullsize helo - it turns out that the quadcopter approach becomes more expensive than a single-rotor AND it's far less efficient.
Kind of similar to how LEDs dominated the flashlight industry for years but only recently became feasible for residential/commercial lighting - incandescent bulbs suffer significantly reduced efficiency and bulb lifetime when scaled down to flashlight sizes.