The best outcome would be to have some Non-commercial organization funded by Google, Microsoft, Yandex and other big players who benefit from Chromium which would have some kind of independence. But current situation is not that bad.
There are other things than just source code license. May be Google has patents for Chromium sources and could use them to forbid fork? Then it's a bad situation but I didn't heard about that point of view yet.
Consumer brands are not as easy to fork. If Coca-Cola opensourced their recipe and then faced a fork by Examplesucre, I don't think anyone will really be betting against Coke.
Similarly, the longevity of mainline integrity for Linux relies heavily on the fact that it is a trademark and that the trademark holder (Linus) is trusted with it. Fork Linux as much as you please, basically nobody will care.
Google's power over Chromium comes from its power over Chrome. If you don't think that's true, fork it yourself and prove us all wrong.
Last I heard, Android was doing OK…
Similarly, I should think that Microsoft still has considerable clout in what browser Windows users will use by default (although I'm not sure what exact legal restrictions they currently have to observe re: bundling of browsers).
Because a majority of users are using Google Chrome.
You're right, if Microsoft could convince chrome users to switch to Edge, they would have more power. Things can change, but I don't see how this would happen.
I've been hoping they'd come up with for a more shared model for applications in the node/npm ecosystem similar to Adobe's Air. If MS did a good job of such a platform from open-source with tooling to build applications that run everywhere, more power to them.