I did an analysis using webpack bundle analyser.
Here is the html report
js/cx.lib.js - the chunk which contains our dependency libraries has core-js being a significant part. This is due to browser pollyfills required to support the range of browsers. Tightening the browserslist configuration strictly reduces the libraries, but will not remove them completely. i18n library is another part - mostly contributed by language data in it, but worth looking whether it can be optimized further.
Explicitly exlcuded IE11 from supported browsers and there is a gain in bundle size now since some polyfills are removed. . New report:
Total gzipped bundle size changed from 129.18 to 109.74 KB