"If other browser engines were allowed in iOS, Chrome/Blink would take over the web browser market"
Pick one, folks. Either Safari is the best, in which case the WebKit monopoly is unnecessary; OR the iOS monopoly is the only thing preventing users from switching to a better browser.
It doesn't matter if you like PWAs or WebUSB. Or what you think about new web standards. The best browser is the browser regular users choose to use. Good web standards are standards that enable sites/apps that users want to use.
Right now, we don't know any of that because the lowest common denominator for the web is not what users want, but what Apple allows users to have. Claiming that those two things are the same sounds a bit weird to me.
It's surprising that people think that Chrome pushing web standards forward means that "everyone has to do what Google wants", while the only true gatekeeper between users and developers these days is Apple's iOS policies.
If you think that's not true, please answer: if a user in any configuration (device+os) WANTS to access your app and you WANT to develop for them, what set of device+os are mediated and by whom? Whose policies you MUST follow to have access to a (major) set of users?
(disclaimer: I'm a Chrome blink engineer involved in web standards)