I'm not convinced that's true.

I do agree to the extent that things like PhoneGap do result in compromises. But React Native is basically a templating tool for native apps – you're still free to write whatever native components you require, but can compose these using React, which is pretty cool. You can then abstract the higher-level components across platforms.

Why would I want to compose native using React?

Probably nothing for the regular mobile-dev. But many of the web-devs can leverage their JS knowledge and hit the mobile-market without "web-container-apps".

Well, that is the point actually. React doesn't put itself as a "write once, run everywhere" kind of solution. What's being offered here is better interoperability between native and web components. The core philosophy is still "learn once, write everywhere".