Then how would something like react-redux work without context?

As people adopt external state containers, like Flux and Redux, it becomes increasingly impractical to bucket brigade chunks of data and callbacks to the leaves of the component tree via props. Some sort of delivery mechanism that doesn't couple in intermediate components is pretty critical to avoid having to maintain an unbounded amount of glue code. Context isn't without its kinks, but it's pretty useful in cutting boilerplate and decoupling components. The one thing I don't buy is that it's somehow worse than props from an architectural perspective (it's often compared to global variables, which makes little sense to me).