If you're looking at training costs, there is definitely one aspect in which LLMs are obviously significantly less efficient: the amount of information needed for the initial training. This does translate into some pretty high costs but it only needs to be paid once for the amount of work that any given LLM does. In terms of fine-tuning LLMs can get significantly more data-efficient than the initial model, which also means energy-efficient, and it's not obvious to me that it would be drastically worse than a human (though again, only thinking in terms of doing the energy input for the kind of work that an LLM is good at).
(The increased efficiency in comparison to humans is part of the reason why you see Jevon's paradox mentioned a lot whenever concerns about the resources used by LLMs are mentioned: more efficiency can easily mean more resource use in total)