tl;dr After failing with webpack tree shaking, I gave rollup a shot. Unfortunately, it's not working here too.

The test case is a simple app with React & React Router v3. Link component is not used, but the whole router package is bundled.

import React from 'react'
import ReactDOM from 'react-dom'
import { Link } from 'react-router'

ReactDOM.render(
  <p>Hey</p>,
  document.getElementById('app')
)

Webpack & Rollup test repo