[endorphone]

I don't think anyone heralded it as revolutionary. It's an affordance to the reality that it's a different experience using devices in darkness than in brightness. Mobile screens make dark situations more prevalent.

As to UI customization, often that was an inconvenient cop out not a great enabler. "We don't want to figure this out so just change things yourself, but then you'll switch PCs or reinstall and you'll lose all of those customizations and you'll never do it again and you will forever leave everything vanilla".

Is it worth websites making a big deal about? No, not really... At most it should put a little badge when it detects the dark mode CSS allowing unwilling users to disable it, but it doesn't seem like something that gets dragged on as long as it has by a couple of sites.