[TeMPOraL]

'TheOtherHobbes offered a detailed reply, but I'd like to add a useful mental model for such questions. Like all other EM radiation, radio waves are just light. They diffuse a bit differently than visible light due to much longer wavelengths, and different materials are transparent/opaque to them, but to a first approximation, you can view the transmitting antenna as a lightbulb, and the receivers as opaque and weakly-reflective objects.

Your questions are thus similar to asking, "If you put a tiny solar cell on a glass table, wouldn't that steal light from the lightbulb? Wouldn't we need a more powerful lightbulb to illuminate the room? Isn't this energy transfer extremely inefficient?". Yes - it consumes some power; no - it casts a tiny shadow, and enough light is scattered around that you won't see the difference; yes, if the only reason you turned the lightbulb on is to power that solar cell, it's very inefficient.