Cross origin browser cache is a no-go for Safari (and hopefully other browsers will follow suit), 3rd party scripts from a CDN are not cached across different domains.
The only way to properly cache things longterm is with webpack records, but not many people can bear with the added complexity of maintaining them in their pipelines.
+1. If you're only targeting evergreen browsers you can already use syntax like `import Library from './library.js'`, plus lots of modern ES6 features.
For IE11 just load polyfills and let the 2-10% of IE11 users pay the tax, instead of making all your users in modern browsers download giant bundles.