Have you tried riot? Or mithril? Small and simple.
Regarding react I don't think there is anything in react itself that says that you have to use es6 and an advanced module bundler (like webpack). Just use es5 code, place everything in one file or just concatenate the files before using them in the browser and everything should work. You mainly loses out on how easy it will be to copy from tutorials that are written for es6 code with modules, and that some 3rd party things are written as modules.
Regarding react I don't think there is anything in react itself that says that you have to use es6 and an advanced module bundler (like webpack). Just use es5 code, place everything in one file or just concatenate the files before using them in the browser and everything should work. You mainly loses out on how easy it will be to copy from tutorials that are written for es6 code with modules, and that some 3rd party things are written as modules.