So like: open display menu -> push some crappy buttons to get to the brightness control -> enter brightness control -> dim brightness -> exit exit -> alt+tab -> use site -> alt+tab back to a dark application -> up screen brightness using the same process -> repeat? Most things I use are set to dark except HN and MDN; dark works day and night (perhaps not in bright sunlight, but I don't code on a beach).

Which is not to say that I'm suggesting we need to have only dark mode, or dark mode by default, or any such thing that you might not be happy with. I'm glad you don't experience the blast of lumens at night, but it seems you're the lucky minority so I'd be happy with an option to set a dark mode.