50-100W for equivalent work as a phone from 2020 can do would have been the case with CPUs from at least a decade ago. I should hope that one doesn't burn ~75W to host a few static files if it can also run on a Pi or phone or laptop that draws <20W idle

That's not to say it's not a good idea to make use of the super efficient "Pi" you already have at home in the form of (several, probably) old smartphones! Just that you'd not use it for the same purpose as a gaming desktop that can't idle below 50W