Exactly right. Aviators know that a propeller blade provides thrust/lift but also induces drag. Given a certain power output, the more blades you have, the more drag you have, but you don't get any more lift/thrust. Therefore, if efficiency is what you want you really want as few blades as you can get away with. Normally more blades are a consequence of other design constraints, such as how wide you can realistically build a propeller blade before the stress causes it to disintegrate.

Small multi-rotors have to spin faster to compensate for their reduced efficiency, leading to the characteristic drone sound.

Computer cooling guys know this too... bigger slower fans move more air and do it with less noise.