Don’t know if it’s unmobile per se. But it’s heavy, JS wise, tends to promote SPAs, and can be quite tough to get to play well with a hybrid.
The react team seems to put their effort in React Native. And that might the only framework I’d never ever ever “touch” again - pun intended:)
We do use react for some mobile stuff, the issue seams to be that you still need a lot of other stuff and your app/UX still feels a bit like a 2nd class citizen