I’m not really understanding the crux of it. Even if archive.is doesn’t get your location via DNS, won’t they get it anyways immediately one millisecond later when you issue an HTTP GET request?
The EDNS client subnet feature reveals the clients subnet (but not entire IP) to the nameserver that answers the DNS query, which is then cached by Cloudflare/Google. This allows the nameserver to do geolocation at the DNS stage and direct the end user to a server with minimal latency.
Without EDNS client subnet, you could get the IP for an archive.is frontend in a different continent and have a slow site experience. While the frontend server will get your IP, it's too late to do much about it under normal circumstances. An HTTP redirect would cost time, and you'd have to have different domains for each data center/region which is one thing you can avoid with the client subnet feature to start with.
You can serve UDP services (eg DNS) by anycast, but if you hosted a tcp service, there's no guarantee the same server would receive consecutive packets from the tcp stream
https://vincent.bernat.ch/en/blog/2018-multi-tier-loadbalanc...
https://blog.cloudflare.com/high-availability-load-balancers...
https://engineering.linkedin.com/network-performance/tcp-ove...
How do CDNs work without controlling DNS resolution by source subnet?
Not if you're using a VPN in addition to Cloudflare servers.