I'm an aeromechanical engineer, not an electrical one, but I suspect the fewer-cells design was chosen to save weight. Many unconventional design decisions in aerospace (everything with holes, novel materials which trickle down to cars and golf clubs) are driven by the need to reduce weight.
These systems replaced hydraulics for surface control, right? On a weight advantage? Making good on a decision like that is exactly what confirmation bias is all about.
The hydraulics are controlled exactly the same as any other fly by wire aircraft like the 777 or a modern airbus. The computer takes the pilot inputs and combines them with a flight computer that controls electric motors which move the flight surfaces with hydraulics.
The big increase in electrical supply (4x over the 777 i believe) is the result of the bleedless air architecture that boeing chose. There was a big push by boeing to make the system work as it was a selling point for the public and carriers. I think that decision didn't receive the scrutiny that it probably should have.
