To me it seems obvious that React would be hierarchical. It is a view layer that creates a virtual DOM, that then gets rendered down into the browser DOM. Which

To me it seems obvious that React would be hierarchical. It is a view layer that creates a virtual DOM, that then gets rendered down into the browser DOM. Which is hierarchical. Horizontal message passing is really a state related issue and lives outside of React. You can manage your state however you want and then wire up the components however you want. Since those two things are separate concerns. Although there are a ton of options in the ecosystem to do that.