It's whack-a-mole, but better whack-a-mole to learn-to-love-the-mole.
Another way to think of it besides the futility of whack-a-mole is, it's pushback, resistance, sand in the gears. It's making an undesired behavior less valuable. Yes you didn't stop sites from including analytics, yes tomorrow google will have some counter move, but that doesn't mean the effort was pointless. If you can exert a 5% pressure on some system and maybe only get a 5% reaction, that's perfectly fine.
It can also be used like the traditional GTM model, where it loads the primary GTM script browser-side, then that loads additional browser-side scripts based on the tags you implement (GA, Facebook, chat systems, map widgets, whatever). But the default GA support built into it avoids loading anything from Google's domains directly by the browser. And it's not even subject to the CNAME cloaking protections[2] that ITP have implemented, since it's not using the "CNAME to third party" technique that's typically common for these sorts of things to get first party access/privileges and is instead actually running on your infrastructure.
[1] https://developers.google.com/tag-manager/serverside
[2] https://webkit.org/blog/11338/cname-cloaking-and-bounce-trac...
I imagine the opposite is true, in that they hold so much power they can do as they please.