They can push technologies that benefit their ads business (e.g. manifest 3 breaking ublock origin). And the notion "embrace extend extinguish" was practically invented for circumstances like this, of engaging the development community in a particular field of software, dominating it, and achieving leverage to change the way the web works.

>that having a lot of stakeholders prevents Google from unilaterally applying unpopular changes

Google controls commits to Chromium, and it does that with an invite only developer pool almost entirely of people associated with Google. The stakeholders don't have a proportionate hand in the destiny of Chromium. I think you're right that it's maybe better, in the sense that we could imagine something even worse, but that's loo low a benchmark to offer comfort that Chromium is having a net-positive impact on balance of power in terms of who can help you access the web.