I think the person you are responding to would say that edge is just another chromium skin. It doesn't exactly relieve Google's monopoly on browser technology

It should fairly simple for MS to block this API (if they wish to).

depends how the api is designed. If it'll be integrated deep into chromium, disabling it would cost too much time

I don't think so. Even if it's impossible to exclude it from the builds, they can just remove it from the JavaScript global scope or something.

Why would they? They make money with ads too

But Googles makes way more, will make compete with Google even harder in the future (deeper pockets).

another chromium skin with extra tracking. I believe Edge tracks by hardware ID more aggressively than Chrome or chromium.

Edge is just chromium. It is not a competitor.

With few exceptions the browser market is a lot like the Volkswagen Group. They design key components and depending on market segment they slap a Audi, VW or Skoda label on it, do a few tweaks to the look and feel and add a few features that they know that a particular segment wants. Under "chrome" it's a Volkswagen.

That's just exchanging one demon on your shoulder for another.

Microsoft is exactly the kind of company that would throw its full backing behind this google proposal, seeing how they have spent the last 20 years working towards the same goal. See Windows 11, Trusted Platform Module, Palladium, SecureBoot.

Not only is Edge based on Chromium, as a major operating system vendor with strong influence on the hardware market, Microsoft is well positioned to be one of the widely-accepted attesters. So they have little motivation to oppose this proposal.