The selling point of BIAB, to me, is the simplicity of it all. Add grains to a bag, dunk in the pot, mash, remove. Done. One pot to clean, one volume of water.
Obviously, you can add all kinds of steps to that routine to try and improve efficiency, but every added step is one step further from the beauty of the process.
I would only get hung up on efficiency if it were inconsistent from one brew to the next, a point already driven home earlier in this thread.