I do understand your concerns regarding safety, but not having WebUSB does not guarantee that malicious websites can't access your USB devices. Both Firefox and Chromium already interact with your USB devices to provide features like debugging over USB, so malicious websites that exploit browser bugs are able to talk to your devices either way. And if we don't count browser bugs, you can simply set your browser to block WebUSB by default to arrive at the same outcome.

Of course there is a chance that specific exploits could work in one case and not the other, but that's something the real-life statistics haven't shown to be an issue so far. Browsers are generally pretty safe these days due to multiple layers of sandboxing, so I'd be surprised to see major WebUSB-specific security exploits appearing in the future.

Edited to add:

Sorry, when I said "sky is falling" I meant a general erosion of user security and privacy, when using our "own" devices.

Same here, I hate the direction things are already clearly heading towards on mobile, and I expect desktops to get enshittified as well soon enough. But I see WebUSB as a major positive in that context (since it allows users to take control of their devices in a much easier and safer manner, & mostly guarantees backwards compatibility of such tools for many years to come). And although I've read comments similar to yours many times - this topic gets brought up fairly often - nobody has explained concrete technical issues that are likely to bite us.