>There's no reason a similar system couldn't be built to deliver platform-native applications

I'm very into the idea of HTML/CSS/JS on the desktop (and by extension, things like react native), even if simply as a frontend to a heavier duty application running on localhost. I feel like the OSs should be shipping runtimes for it instead of having insane 120MB hello world electron apps.

Web apps also don't necessarily mean someone else has control over your data -- it is technically easier to determine whether they do. You can inspect web requests in your browser, you can't in most native apps. There are plenty of silly things like Dark Souls stat calculators that make so much more sense as a webapp, and are 100% client side.