Where this gets confusing to some modellers is the situation where they change to a multi-blade prop & their speed goes up or their climb goes up. In those cases, they were under-propped with the 2-blade.
At low speeds yes. But at high speeds you will get more thrust from a smaller column of air with a higher velocity than a larger column of air at a lower speed. That is why you will find more and more blades on the large Reno racers. Sure it's less efficient, but going fast is always less efficient than going slow!