> Even WebRTC is a bit of a stretch
You remove that, and videoconferencing (for business or person to person) has to rely on downloading an app, meaning whoever is behind the website has to release for 10-15 OSes now. Some already do, but not everyone has that budget so now there's a massive moat around it.
> But do we need e.g serial port or raw USB access straight from a random website
Being able to flash an IoT (e.g. ESP32) device from the browser is useful for a lot of people. For the "normies", there was also Stadia allowing you to flash their controller to be a generic Bluetooth/usb one on a website, using that webUSB. Without it Google would have had to release an app for multiple OSes, or more likely, would have just left the devices as paperweights. Also, you can use FIDO/U2F keys directly now, which is pretty good.
Browsers are the modern Excel, people complain that they do too much and you only need 20%. But it's a different 20% for everyone.