This is a good point that tends to get drowned out by the severe privacy and security concerns. WebUSB provides zero value to the overwhelming majority of end users, and minimal value to the handful of us who have ever used it at all.
This is why it is contentious: On the one hand you have a great QoL benefits for a minority of users who are more than willing to accept the potential fingerprinting risk and consider other dangers to be overblown hypotheticals, or are technical enough to mitigate those issues. On the other you have the vast majority who have no need of the feature at all, and are probably unaware of any risk and will be until it becomes apparent in a can't-be-undone manner. Google sides with the former, Firefox and Apple err the other way. At what point a small potential risk for everybody is worth QoL benefits for a relative few, is the main point of contention (the second largest probably being a mix of “is the risk really a risk anyway?” or “but you'll be fingerprinted to buggery & back anyway so what difference does this bit-or-few of data really make?”).
A side issue is the concern about the browser becoming a bloated almost-but-not-quite full OS, and a huge mess that needs much effort to maintain to keep its growing attack surface defended.
To a relatively small group of enthusiasts, sure. I'd love to see numbers on the percentage of browser-users who own keyboards which require regular firmware updates..,
The use cases for extensions cover a much larger segment of browser users than programmable keyboards and microcontrollers though: there is a lot more mass appeal for things like languagetool/grammarly, ad-blockers and other page tidiers, tools that are useful for devs¹, and so forth.
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[1] I'd put money on even the vast majority of front-end devs not touching microcontrollers or having programmable keyboards.
Pretty much everyone involved in the security and usability of the internet.
Enthusiasts will find ways to accomplish what they want to regardless of whether there's an easy browser-based path.
Blink, WebKit, and Gecko devs probably.