These, and/or lack of deep integration with platform's UI features (e.g. keyboard shortcuts), and/or UI occasionally blanking out with 404 or 500 page because of networking problems.

Yes, you can usually tell webapps from native apps apart pretty quickly.

While I agree with you, it is also a consequence of not doing proper testing.

I have used a couple of native apps that crash on network problems, and in some cases they just vanish from the screen on crash without any OS dialog coming up.

I rather have to deal with mobile web apps than web widgets, specially if I have to code them.

The app accessing your contact list, monitoring phone calls, accessing your private photos. That's also how you can tell the difference between a "native" app and a progressive web app.

Even on a modern pixel 3, the slider animation is a bit behind. Everything else looks smooth, but the slider definitely feels "off".

Likewise on my S8, the telltale jankiness gives it away.

Works fine for me on an older iPhone