Nah, the lesson is that users are going to blame you when you make low level arbitrary changes that break things when they're not capable of knowing about and fixing the technical problems that arise. The fact that a change might accidentally fix problems sometimes isn't a counter example to that general principle.
Even when the possibility of things getting fixed is substantially more likely than the possibility of things getting broken?
By default Firefox will fall back to the network resolver if DoH can't get the results, so the only way that a situation like this could happen is if someone purposely sabotages the DoH results like with archive.is.
Furthermore, what you are saying could basically be used to rationalize putting any kind of potentially breaking change behind an off-by-default configurable. Do you think the web would be the sophisticated application platform it is today if browser vendors actually had that philosophy? Would that actually be better for John Doe, to make them have to learn about the technical aspects of every new web technology before they are able to take advantage of them?
