I have HN and a terminal open side by side, and I can tell you HN is more painful to look at, simply because it's like shining flashlight into the eyes compared to a black-background terminal.
Not for me, nobody looking at my computer except for me and I have Slack now in dark mode, I have Dark Background and Light Text in Firefox (also dark mode) and custom dark style sheets in Stylus where they are available and good.
Maybe it's because I'm getting older, but staring at a blinding white computer monitor inches from my face all day as a software engineer HURTS. Like, literally hurts after a while.