It's not that you're being a downer, you're just not presenting things in a fair or accurate manner.

Google didn't merely "ship a feature someone else didn't". They keep shipping new features as they wish, whether others even agree. They have in fact accelerated that attitude with Project Fugu. Some of them are quite complex or consequential APIs.

They do not deserve a free pass for it because Mozilla once shipped one or two relative minor features before Chrome did, or Apple added some weird CSS visual property for their latest iPhones without consensus. We're talking orders of magnitude of difference here.

The problem isn't who is first to ship. It's the casual disregard for even reaching consensus on the basics before shipping something, the sheer rate of output, the interop issues left in the wake, and the anti-competitive tactics being applied. Those are not "hypotheticals" in the slightest.

What is hypothetical is acting like anyone else could just magically compete on those terms. Microsoft couldn't keep up with them. Opera couldn't. No new engine has even come close to breaking into a general market yet, though a couple are feverishly trying.

Is that really ok with us? If so, then let's just be honest. Let's just say "new APIs are more important to us than engine diversity, and we don't mind Google being as evil as possible to kill the other engines off." As a webcompat worker, I'd love to see that honesty.

Do you think it's abusive of Linux to offer APIs beyond what is standardized in POSIX, breaking comparability with other nix-like OS such as FreeBSD? Or is it abusive that clang constantly adds features that gcc lacks, making programs that use clang no longer compile with gcc?

average disingenuous HNer making comparisons between compilers and web browsers. Everyone involved knows Shadow DOM V0 was a rush job, as was the YouTube redesign that used it (it had major perf issues even in chrome when it came out). The standardized ShadowDOM v1 is better in every way and works in all browsers. It's pretty clear that Google wanted V0 to spread as far as possible so they could force it to become a standard, as removing it would "break the web". Shadow DOM, regardless of version, isn't critical for a product like YouTube. The "web" is only the "web" if parties involved play fair, even just a bit, otherwise it's back to IE6.

Does Linux also happen to control a major piece of hardware pretty much everyone uses, and used it to force BSD to adopt some new driver system they wanted to prioritize, which ended up being completely different by the time the dust had settled, and held back other important advancements in the meantime?

That is, it all depends on the full context. Competition is fine, but not anti-competitive behaviour. I maintain that we have had too much of the latter from Google, and that it is only increasing as folks intentionally look the other way and try to boil arguments away to mere deflections and other apologia.