I think you misunderstood (or don't know what "de facto" means).

> Google don’t unilaterally decide what the web is.

They absolutely do.

They don’t. We are close to that point, yes, which is why it’s so important to clearly delineate what is a web standard reached through consensus from what is Google trying to push their stuff through regardless.

If something doesn’t work in Safari or Firefox then web developers normally still hold back, so they aren’t de facto standards. We aren’t quite at the point we were when IE dominated the web. But there is a growing number of developers who blame other rendering engines for not blindly going along with whatever Google says, and that needs to be stopped in its tracks not accepted.

> then web developers normally still hold back

It takes just a few weeks on hn to see it's not true and there are a few devs who will point to the usage stats and not care about Firefox. For safari, many people just don't have access to it, so they'll never test in the first place.

Hacker News is not representative of the typical case. There are very few professional web developers who ignore Safari – a huge number of people surf on mobile and a huge proportion of mobile users are Safari, so any developer ignoring them isn’t doing a very good job. All web developers have access to Safari – if they don’t use macOS then they use a tool like BrowserStack to test in Safari. This is a standard part of a web developer’s toolchain.