This is correct - any “Chromium-based” browser is literally a fork unless it’s completely unchanged from upstream (even rebranding and changing the logo and name would require maintaining a fork).

Sure. And the further a fork diverges from upstream the more difficult maintenance becomes. My point is that relying on the open source model to fork projects making hostile changes only works so long as the community is actually able to maintain the fork(s), and so long as those forks actually have a reasonable chance of being adopted. It's equally important, if not even more important, to try to ensure these large projects steer in consumer friendly directions than to react and fork to try to remove anti-consumer features.

Google has enough market and mind share that they can push this and it's a real risk of becoming an anti-consumer standard regardless of any attempts to maintain a fork.

So what do I think we, as a body of users of the Internet, should do? Simple. Stop using Google Chrome and any other Chromium based browsers. Google has the ability to push these changes and make them defacto standards (and later, codified standards) because we collectively give them the power to by using Chromium downstreams.

That may be true, but it's a fork where I doubt any company has the capability to do the engine development needed to be totally independent from Google. There is a reason Apple and Mozilla are the only two alternative engines left. It costs a lot to develop a browser