It's the same situation as gold and gold mining. The marginal cost of gold mining tends to stay near the price of gold. Gold mining is a waste, but that waste is far less than the utility of having gold available as a medium of exchange.
I think the case will be the same for Bitcoin. The utility of the exchanges made possible by Bitcoin will far exceed the cost of electricity used. Therefore, not having Bitcoin would be the net waste.
The cost of proof-of-work is not merely equal to the power used, it is indeed equal to the mining rewards - $557,358,000 annually at today's quoted price.
I concede that this is a lower figure than the 10% of the world's economy consumed by the financial sector, yet it is a waste because Satoshi could not conceive of proof-of-stake, nor did he debate the concept. The existing idea of hashing proof-of-work instead was adopted for Bitcoin.
I believe you are correct he didn't debate the the topic but I believe he saw the problem of energy consumption and introduced a diminishing return.