pedestal is quite a large project, try to offer a complete solution for building web application in Clojure, from server side to client side, to tooling.
http-kit is a very small and focused library, It just do one thing: talk in HTTP. http-kit need to work together with other libraries like Ring[1] and Compojure[2] to do the server side.
Few good things about http-kit:
1. Very fast and scalable, almost as fast as what you can get from the hardware.
2. Focus, do one thing and do it well, thing about Linux/Unix's philosophy. Personally, I prefer this way of doing software.