I haven't see that thread, but I suspect that depends on how we define efficiency. It might be so if we define efficiency simply as potential energy converted into work. But if the potential energy requires a lot of preparation to get it into position to be converted (e.g. mining, transportation, peripheral energy the miners themselves use to get to work, etc.) then it might not be as efficient as using an abundant source of power that's happening whether we use it or not (e.g. solar, tide, wind, etc.)
And, of course, pollution might come into play too. If your efficient power just also happens to emit toxic smoke, then efficiency may be the wrong criterion to look at.
I'm reminded here of the hydraulic ram. For those not familiar with it, it's a pressure pump using a low pressure head of water to power an impulse pump that moves water at high pressure. In one sense of efficiency, its awful. It wastes most of the water that passes through it, in order to pump a small amount under pressure. But in another sense of efficiency it's unbeatable. In a place where water is flowing downhill anyway, it does its job with no added energy at all. It all depends on how you look at it.
