I've been seeing incredibly compressible output from Typescript, if that helps any. If what you mean by 'bundle' are these 'webpack' things that include css and images, and all that. Smaller bundle to me would be not to use one at all.
It doesn't seem like webpack's chief concern is file size or simplicity. So if yours is, just don't use it.
Babel can parse Flow, which is similar to Typescript. However, Babel doesn't have any built-in support for inferring or analyzing flow types. However, some of this type information might be useful in building a more advanced closure-like minifier.
