I don't think every Aereo subscriber requires a dedicated transmitter. Aereo depends on the existing Internet infrastructure, be it wired or wireless, to reach its subscribers. So whatever transmitters are ultimately used to reach a client are those already deployed by wired or wireless ISPs.
Aereo does provide personal DVR services "in the cloud," as you point out, which would concentrate power requirements at their facilities. But hey, this is very much the same as what cable companies provide when they sell you in-system DVR service. That too concentrates power requirements "in their cloud."
Agree completely that over the air broadcast is the most efficient way of getting wide bandiwdth to a practically unlimited number of people. However, any non-real-time viewing is only possible with PVRs at the customer premises, and of course, one-way broadcast is limited to one-to-everyone data flow. So it can't also be used for Internet connectivity.
My only question about Aereo is, shouldn't they be redundant? The networks already have a presence on the Internet. That's how I watch most of my TV anymore. The networks provided their programs only ofter the fact, on demand, not live, but that's purely their decision. So if the networks, and/or their affiliated broadcast stations, also streamed their TV signals live, that would make Aereo unnecessary.
People want TV over the Internet these days, is the bottom line.