Its definitely true that you can key responses to request information beyond the URLs, but I think theres more to it than this:

- Lots of tools don't allow you to block requests off those additional keys (Google's Manifest v3 for one, Apple's iOS content blocking too)

- In many cases, making consistent replies based off those keys requires additional information privacy tools also try to limit (referrer fields, cookies, etc)

- There is practical, real world value in making things more difficult for trackers / folks sending you stuff you don't want; decisions are made at the margins!

- Ad blockers are common on the web (estimates 10-30% of users!); they're effective bc they work with the grain of the web, and circumvention is deterred (though not prevented) bc there are costs to circumventing adblockers; WebBundles push those costs to zero. Again, decisions are made at the margins