Hold on - do you know what a progressive web app is? We're not talking about apps like Slack which bundle a browser inside of them - we're talking about webpages that behave like applications.
>many vendors do not care about making their webapp work correctly when connectivity is limited, spotty or lacking.
Offline support is a key feature of PWAs, so this point is moot.
>Each operating system has a large set of default UI behaviours and idiosyncrasies.
Browsers are completely able to define their own design language, so a text box need not look the same in every browser. As long as they conform to common standards, everything will work fine.
As such, you don't get the Java problem where everything must conform to the same style, and thus feels foreign in different environments.
>I want my applications to be performant, platform-consistent and interoperable. Web apps fail at all three
PWAs excel at all three. That's the whole idea.