Even assuming they did make development decisions to benefit advertising partners, how on earth would choosing not to optimize performance actually benefit them?

That’s what it sounds like to me, but it’s a bit unclear admittedly.

Yay!

In many cases you can, but there’s never a guarantee that a given IP address will have reverse DNS records configured for resolve it into. On top of that, if it’s a major site it’s likely hosted behind a content delivery network that may a share a single IP address across thousands or even millions of completely unrelated servers. Cloudflare does some pretty interesting stuff with that approach: https://blog.cloudflare.com/cloudflare-servers-dont-own-ips-anymore/ edit: bad at typing

This makes it so that your ISP doesn’t see the actual name of the server/site you’re communicating with, only the IP address. Without Encrypted Hello they’re able to see both.