Hi Jenya,
this is not really an issue, more an question.
In my fork I updated all npm packages including babel, webpack and core-js.
After the build-release I released that the size of widget.js increased to 130 KB.
After setting useBuiltIns: 'entry' or removing it, the file size became smaller, but still 79 KB.
Do you have an idea how to get the size significantly reduced?