I think you are severely misunderstanding the situation. Google can do whatever they want. They've already demonstrated that they have no problem installing things on your computer that you never would have otherwise agreed to. That, and they don't take no for an answer with updates.
Do they? I just downgraded Chrome for Android to 56, because the latest one would crash when playing live video streams. Granted, Play Store didn't have that option, so I had to download the APK from a third-party site and disable automatic updates for it, but nothing prevented me from doing either thing.
Yes, you still can on Android. But Google has shown that they don't see anything morally wrong with using misleading updating tactics. And the range of what you have control over is shrinking.
These privacy forks generally lag behind upstream by at least a few weeks, thereby providing enormous attack surface in unfixed bugs. They're terrible for security. Chromium is just too large and fast-moving for a small team to maintain a changeset. I'd love if it was different, but the reality is that these forks do more harm than good for most users.