This elides an important detail: outside of iOS a browser implementer can choose the code to compile and link against. Even if they build on Chrome, they can patch it to their heart's content or even fork and carry on. On iOS the browser runtime is set by fiat.

Also worth observing that most web browsers in the history of the web (including Chrome and Safari) started out as a fork of some other browser.

I think so too. Talking about monopoly and then participating in advancing a de-facto monopoly (Chromium on Android and Chromium on Windows)