> Enterprise use cases can easily manage this through Group Policy.
That's Windows-only mechanism.
> Households (keep in mind we are only talking about people who knew enough to change DNS settings in the first place) can just change the setting on each of their five or so computers.
And not forget to do that for every new device they get. And after reinstalls. And occasionally just to be sure, as we know how software tends to "forget" user preferences sometimes. That's all only up until Mozillas' telemetry will show, that nobody changes the default anyway, so the preference will be removed entirely.
> And if you are using DNS as parental controls, that's not a great solution as nothing stops someone from getting the IPs out of band (ex. a website that does DNS lookups) and connecting directly to the blocked sites.
For the user, it's more complicated than that. He has to persuade the browser to send the right Host header when connecting to the obtained-out-of-band IP address. If you have rights to modify hosts file, you might change the DNS as well and spare the effort.