I haven't touched browserify, but with webpack what you said could not be more false...
Webpack doesn't bundle at runtime, it doesn't add any amount of code overhead per module that I can easily measure, and it doesn't trash startup speed.
Same goes for browserify. You can have lots of tiny modules and (watchify especially) is fast to re-build. And yeah perf of 'require' statements at run-time is a non-issue.
Webpack doesn't bundle at runtime, it doesn't add any amount of code overhead per module that I can easily measure, and it doesn't trash startup speed.