Just out of curiosity, why not use a conditional polyfill using nomodule rather than outright breaking on something like IE11? Because we use nomodule, the script tag will be ignored by modern browsers, while IE will fetch the polyfill. polyfill.io serves this request, and we have it include all the polyfills we require (for our use case, we just request the default plus es2015-16-17-18, plus fetch).

The beauty of the approach is that the big pollyfill payloads are only borne by the users who choose (or likely are forced by employers) to use those browser versions.