The benefit hooks bring is that as well as already being able to separate out components, you can now separate out React functionality into reusable pieces in a clean way.
It's not about making something possible; it hasn't introduced any new capabilities. It's about improved semantics.
Everything that is possible with programming has been possible since we were poking hex codes directly into memory. All language improvements have been about semantics, or fixing performance degradations brought about by new programming paradigms.
[edit] I do agree that mixins could've been good too.
