A machine that spits out one widget per watt is less efficient than a machine that spits out 10 widgets per watt. Even if there is exactly one widget machine in

A machine that spits out one widget per watt is less efficient than a machine that spits out 10 widgets per watt. Even if there is exactly one widget machine in the world, it is always turned on and always draws the same amount of energy, one type of machine would produce more widgets than the other. That machine is more efficient. It is more useful for the same energy input. It's a totally reasonable metric to compare widget-producing machines by! If the bitcoin network is a transaction-producing machine, the more energy it takes to produce the same number of transactions, the less efficient it is. All else being equal, spending more money and energy for the same result is worse than spending less money and energy.