Useless is a strong word, and "absolutely" is a strong modifier. Neither is warranted here.
Point taken. I've held an amateur license for 25 years, and the nature of the gear people own and operate has changed a lot. I question how useful a gaggle of people with low-powered VHF gear at low altitudes will be when information needs to be passed around a metropolitan area after the local repeaters have run out of juice. Thanks to HOAs, It's difficult for the average urbanite or suburbanite to operate a station that covers the HF bands that are most effective for local and regional communication (40m and below). It doesn't do any good if the nearest guy who can get away with the required antennas is 40 miles out of town.
Meanwhile, those people are likely to have disconnected power sources...
No more likely than the average person. I'm pretty sure I'm the only licensed amateur on my street, but looking out the window I count a few dozen pre-fueled, fully-mobile, disconnected power sources that can be pressed into service on a moment's notice. All of those sources have built-in AM and FM broadcast receivers (some have satellite receivers, too), internal and external lighting, weather-tight shelter, lockable storage and sources of heating and cooling. More on topic, they can be used to charge mobile devices which, even without the network available, stuff a fistful of things that can be useful in an emergency into a very small package that the average person knows how to operate. And most people already own the necessary cabling to do that charging and keep it handy.
...many radio stations are in urban areas and are legally prohibited from having inexpensive, functional backup power.
Can you cite a source for that kind of prohibition?
There's already a surprising amount of generator capacity in the average city and lots more that can be trucked in and functional in relatively little time. I used to work for a commercial FM in an urban area, and our building (downtown) had enough on-site backup to operate the studio and microwave link to the transmitter for several days. The transmitter (outside the city for coverage reasons) had a generator which could run it at full power as long as there was fuel available. I'm pretty sure the station had agreements in place to have fuel available at both sites within hours if needed.