Yep you have some good points to consider anon. Good engineering is all about balancing trade-offs, and picking the correct subset of possibilities to optimize.
>We need to go smaller, into SBC and embedded stuff
Absolutely this. For both size, weight, power consumption, heat generation, and cost. Amazingly all these are feasible in SBCs readily available on the market today–and they're pretty powerful too! Almost too good to be true tbh. I have both the Beaglebone Blue, Beaglebone Black Wireless, and Raspberry Pi 2b, and plan to get an Arduino R3 shortly. The Blue is expressly designed to support robotics and has a large number of connections and capabilities already onboard. For example you can literally run 8 different servos with one of these. This also happens to be exactly the number I need for each of the dexterous hand designs I'm working on, and there is plenty of networked processing power onboard I can also tap into for other uses beyond just running a hand.