> Using subresource integrity "random-js-library" hosted on a 3rd party isn't "arbitrary code execution", as the useragent will refuse to run the script if it's hash changes in any way from what you provided.
That's true, but SRI is still rarely deployed; and no surprise there: the official Google docs don't use SRI in their "paste this into your code" examples: https://developers.google.com/speed/libraries/
Also, Edge still doesn't support SRI.
So, yes, for some UAs this specific problem (resource integrity) is a solved problem, but like I said, it's far from the default.
The other issues - lack of necessity, load time, degraded visual quality, giving user data away for free to an advertiser etc. - remain untouched.