[nchmy]

It doesn't actually fail to protect 5%, as the top-line 5% aren't really "browsers". Even things like checkboxes often top out at around 95%!

You can change a setting on caniuse.com and it excludes untracked browsers. Sec-Fetch-Site goes up to 97.6, with remainder being a bit of safari (which will likely update soon) and some people still on ancient versions of chrome.

The fallback origin header goes to 99.8 coverage.