> lowers the amount of energy spent on mining

I don’t see how that part follows from the rest. It makes sense that electricity consumed per time overall converges on the block reward plus tx fees per time. Since the reward is so much larger, energy consumption per time scales with price. Checks out.

But doesn’t the same apply to BCH? If the tx fees are even lower isn’t the block reward even more dominant, and so energy consumption should track price even more closely for that chain?

Also, showing my lack of knowledge about the specifics of the protocol - is the amount of work done to compute each hash really constant in the number of transactions in the block? Or just negligibly different at current tx volumes?