If Microsoft, Apple, and Google all disagree with WHATWG or W3C, they're winning regardless of whether or not Firefox exists.

The second scenario is just repeating the problems with Chromium.

In theory, if one engine was agreed upon as ideal and collaborated on fairly, the other parties could just fork it and maintain that branch separately from the usurper and make that the standard.

The hypothetical here is FLoC.

If everything were based on Chromium, and Google really wanted FLoC, how would that play out?

They'd add support to the codebase and... what? Everyone else would fork? Or how about for DRM support?

It's the "collaborated on fairly" that's the difficult and unsustainable piece. Especially when we're talking last mile things (i.e. that interact with the user) and the additional rewards those entice less altruistic parties with.

Java/Oracle/IBM is what you realistically get when there's serious $$$s on the table and multiple parties. And that's probably about the best possible outcome.

Does this criticism also apply to the Linux kernel? Which is as widely used as Chrome on servers?

There's at least Windows, macOS, FreeBSD as popular and fairly used alternatives.

Also, the Linux kernel itself is just one small part of a Linux distro, which means everyone from kernel maintainers, to distro creators/maintainers, to particular app makers have some direct to indirect sway on the kernel development.

You could say the same about WebKit, that it's just a small part of a browser - Chrome/Safari/Edge/Brave/...

Note that Chromium hasn't been based on WebKit for almost a decade. Google forked WebKit and created Blink as their rendering engine in 2013. The two have diverged quite a bit. Safari is the only major browser still based on WebKit explicitly. Chrome, Edge, Brave, Samsung Internet, etc., are all based on Chromium and thus have Blink as their rendering engine.

There are other OSs available though. Including other POSIX compliant OSs

What happens when the Linux kernel decides to ignore standards bodies?

What happens if a single party manages to usurp governance?

"The Linux kernel", in this analogy, doesn't also own a major cloud platform and/or device ecosystem and/or top ranked websites.

I think in the 21st century we should have clearer glasses about what key enablers corporations can leverage to push their visions, even on ostensibly open source codebases.

Google did this with Android. It's GPLv2, 'standards bodies' (and Linus, but he seems to be cool) can go pound sand.