109
Apple already shipped attestation on the web(DRM), and we barely noticed
(httptoolkit.com)
This is a most excellent place for technology news and articles.
Google's proposal also has sites serve content to clients without the attestation, or at least so they claim in the repo (thus the proposal to make the check deliberately fail sometimes, so websites won't rely on it. Of course, there is no guarantee it will stay that way, Google could change that policy whenever they want.
The main difference is really in Google's dominance on the web. Sites can't start requiring Safari, but they can start requiring Chrome or Safari.