Well I MITM myself quite often to confirm it. I’m also smashing together hundreds of blocklists, and I always check the network tab of my browser’s developer tools and very rarely see anything coming from third-party domains.
Sure, sometimes assets are on the actual domain I’m visiting (or its CDN) but most of the time, even tracking scripts there are broken because they still call the blocked scripts.
By the way, it’s hilarious that everyone wants to fight so hard about this yet when someone says “use an adblocker” nobody says anything as if it’s the end-all solution.
I didn’t say “I have a bulletproof, surefire way to fix this.” I said “use network-based blocking.” However effective that is is up to the person implementing it; you have no idea how effective my setup is because you don’t have access to its configuration.