It is hard to say what you call “complex platform”, React is a library, not a framework or a platform (maybe RN is), so I would not consider it as a complex. There are pretty much libraries which are using virtual DOM rendering, I have few options for you:
Deku – a library for rendering interfaces using pure functions and virtual DOM. You write views in a similar way to React (JSX), it looks very similar but more lightweight. You can also make own library based on their diffing and patching API.
virtual-dom – This library originally intended to be as a plain rendering engine, so most likely this is what you actually want.
Cycle.js – Functional and reactive framework, it is possible to use JSX (usually no JSX in docs), but not necessary. You can use it with RN as I know.
Mithril – One more, really lightweight, I use it a lot before I switched to React.
Hope this help.