Re: no real use case ?
Two things: one is that there are reports from people who have checked the math, and they claim that the bitcoin energy consumption is nowhere close to what's been reported. As far as I know there's just one source for the sky-high energy estimates (Digiconomist) and they admit that there's no way to verify their numbers. See for example:
Second, bitcoin and blockchain aren't the same thing, although of course bitcoin uses blockchain technology. Bitcoin mining is CPU-intensive on purpose -- that's a design goal that's central to how it works -- but blockchain systems in general don't have to work the same way.