I think we agree on everything, thank you for expanding your reasoning. > Now if for some reason you could not harvest energy directly from B-C, yes you could

I think we agree on everything, thank you for expanding your reasoning. > Now if for some reason you could not harvest energy directly from B-C, yes you could use water going from A to C to power the pump from B to A, it would just be less efficient. I also think that was the initial point: some higher-efficiency generators ("steam turbine") are only available for high potential differentials. Whether raising the potential offsets the gains likely depends on the specific setup and energy source.