There's probably a dozen versions of react that make up a healthy 20% of the web.
> and in a short enough time to not suffer a cache eviction
These assets are cached by version. They can be basically immutable forever, with maximum expiration.
As commented elsewhere, you don't even have to give away free analytics. Just set a referrerPolicy on your <script> tags. And add subresource integrity to protect from the CDN being compromised.
I get that the Storage Isolation needs forced us to blow up the real awesomeness of CDNs. I'm ok with it. But it feels wild me to me to say that the cross-site caching wasn't worth anything. It was a super excellent path to fast loading, was enormously enormously helpful, especially for the age, when very few people had reliably low latency high bandwidth broadband.