I can't agree with you on that sorry, why take the overhead an put in another tool like gulp or grunt if you can do hardly everything within webpack and npm scripts? Sure, Webpack is a Module Bundler, that's what it's here for, but together with npm scripts it's a really nice way to bundle and build you app. No need for any other tool. Regarding the styles, if you use Css Modules, then you'll have to find some way to parse your styles to, and when you are already bundling with webpack, why not use it to extract your sass files and build a ready-made css file? It CAN do it, and it's no performance loss. Injecting Styles into the head isn't the best thing that happened to the World, BUT during development in combination with HMR it's powerful, and NO other tool can solve this like Webpack does.
Sum: Webpack is powerful, even more in the upcoming V2. There is absolutely no reason to include another tool to be able to build your stuff if you ask me.
Yanni Nightingale
Front-end Developer