They wouldn’t be at the mercy of anything. That’s…how open source works.
That’s how Chromium works.
Anyone can see the source, but it doesn’t mean that anyone’s code makes it into Chromium, because Google picks and chooses. Chromium has a “reviewer pool” of Google developers doing all the picking and choosing. Getting into the reviewer pool takes months to years of building up a contribution history and being vetted by the Google team.
They’re completely at the mercy of how Google integrates things like DRM, or web standards that Google wants to push, like a deeply integrated into the browser and actively maintained with little to no alternative. The engineering overhead of sustaining and increasingly complex fork of Chromium is unsustainable and unless you have the development capability to compete, Google controls the destiny of any chromium browser.
You can’t for a number of reasons. As other people have said this catastrophically underestimates the complexity of maintaining a code base for a browser.
I don’t even think that’s remotely true. My understanding is that it’s on the order of a few months to a year, and it relates to things that are negligible to the average end user. They are edge case things like experimental 3d rendering. The most significant one I can think of is Webp, but they resisted adoption for principled reasons relating to Google’s control over that format and aggressive pushing of it, which is a good thing not a bad thing, and an important example of how rushing to adopt new standards it’s not necessarily just a sign of browser health but also an anti-competitive practice intentionally pushed by companies that have money to throw around for that purpose.