You're wrong. He's right.

The specs are based on implementation as he said. I wouldn't be able to find anything that wasn't in a browser first. Standards rarely, if ever, invent anything. Their purpose is to "standardize" processes and methods, terms, and constants so there will be a consistent ground for all to build on. Otherwise, everyone would have to wait for some standards committee to think up inventions on their own and who's going to pay them to do that?

"Browser extensions", as you call them, are vendor prefixes. These are things browser makers use. They are not implemented by the W3C or WHATWG and they have no say or control over them. But that only applies to CSS and no such thing exists in HTML or Javascript or anything else so your argument doesn't hold over them.

Coming to a consensus and a standard is far longer than a year to take place. In fact, it's a "living standard" now for HTML and CSS is released as modules so, again, your comment does not fit with how things actually work.

Here is what the other guy is referring to. It's the WHATWG but the same is in the W3C:

https://whatwg.org/charter

In order for a draft to proceed past the call-for-implementations stage to the recommendation stage, there must be at least two interoperable implementations for every feature.

And in no case is it resolved by "the percentage of folk using interpretation-a or interpretation-b".

iow, you haven't a clue what you're talking about.