Mining means finding the hash for the next block. Mining empty blocks if there are no transactions is perfectly fine. The expected size of a block makes no diff

Mining means finding the hash for the next block. Mining empty blocks if there are no transactions is perfectly fine. The expected size of a block makes no difference to power consumption. The only relevant parameter is the point at which it becomes unprofitable. You could argue that if less fees were spent, some barely profitable mining rigs would be turned off in anticipation. However, Bitcoin is not at the point were fees are decisive yet.