There is something to be said for using APIs whose total surface area is close to the surface area that you need. If I want to use different parts of three libraries, but those libraries have excess functionality with a lot of overlap, then I have to deal with potentially conflicting expectations. I also have to worry that the subset of functionality I do use will go away or change because it's not the central focus of the library.
The thing is, if you're using a VDOM, you'll probably want the other stuff Mithril's got anyways. And the tight integration with the vdom renderer helps make sure that rerenders happen only when something actually changes, and that partial states don't render. For 3 megs, I'll take it.
