You've just illustrated the advantage of a polyculture: changes to the platform are not unilateral decisions, and therefore require discussion, communication, and documentation. Furthermore, if one actor tries to do something out of blatant self-interest that would be a detriment to the platform as a whole, that action can be blocked. With a Google monoculture, at the end of the day, the web will be whatever the CEO of Google allows it to be. Imagine how little control users have over the Android platform; envision a future where that's the web's model as well.

> You still can’t add a new feature the other side doesn’t want

That's not quite true. This happens all the time with things not standardised (yet). With time those either get wide adoption because people want them, or get dropped, or get standardised in a different widely agreed form.

Your argument is easily proven false by looking at the various CSS properties prefixed by vendors like -moz-* and -webkit-* that eventually made it into the standard.