How is market share relevant?
What would be wrong with designing simple web standards and as a result having 1000 options each with 0.1% market share?
> Super-simple engines that any indie can solo-code
This is a straw man.
> video/audio streaming
There used to be browser plugins for things like this.
> web developers (your audience, remember?)
> users (your "actual" audience)
Which is it?
Catering almost exclusively to web developers, as the browsers have done, unfortunately, is not in the best interest of web users.
> native apps beholden to their own monopolies, that are mostly crappy (contractor-made, less sandboxed/secure than on the current web)
This is false.
> And it means making every company's revenue dependent on Apple/Google/MS
This is true regardless, native or web.
And people like the article author like to claim that Apple is forcing companies to write native apps, but notice that on Android, where there are alternative web browser engines, these same companies still write native apps. That's not because WebKit is bad, because WebKit is irrelevant on Android. Rather, it's because smartphone browsing is generally inconvenient and also native apps offer some inherent advantages over web pages.
To be clear, monopolies are bad, both for operating systems and for web browsers. But turning web browsers into operating systems won't break the current monopolies, because it's the same companies in either case.
The unfettered market has failed. We really need democratic governments to break up the monopolies. Whether that will happen or not remains to be seen.
> instead of a web domain they control.
Do you even "control" a web domain? Web browsers can throw scary warnings over http and force you to adopt https certificates. Then the web browsers can decided which certificate vendors to trust or distrust. And all the web browsers have so-called "safe browsing" that can arbitrarily decide, with no warning and no resource, that your domain is unsafe.