WebUSB is amazing for trusted computation on TKey platform, i.e. you don't have to trust the browser to load the correct program as the key is always DICE-derived deterministically. The browser is the best thing since sliced bread for running all kinds of programs without having to actually install any of them.
I have used WebUSB exactly once: to use the GrapheneOS webinstaller. I keep a copy of Chromium around and use it about once a year for some kind of nonsense along these lines.
I do, but I also benefit from the fact that Chrome is basically everywhere already, so I use Firefox as my primary browser, and just break out Chrome when I need to flash some devices with ESPHome or something.
Who the f needs/uses WebUSB? :D