What do you need that isn't in the box with React? Aside from fetch, which is in all modern browsers? The new Context component interface pretty much flushes out the last of what you are likely to need. As much so as what you get in the box with Angular. Even then, with Angular you'll usually need at least a visual component library, and with React, disparate components tend to work together with less friction comparatively.

Well if you focus on components only in your app then sure, not much needed. But complex apps need much more, like testing infrastructure, routing, data layer, service layer, tons of utility functions (last time I toyed with React it did not even have debounce ... Library for UI w/o it seems weird for me) and likely something else.

But hey, most apps are simple, so no need for all the above. I would say Ng/Ember are more specialized / niche.