Dropping Support For IE11 Is Progressive Enhancement · The Ethically-Trained Programmer
Any time or effort spent getting your JavaScript working in IE11 is wasted time that could be better spent making a better experience for users without JavaScript.
I agree with this approach.
With a few minor omissions and links, you can create a site that works great in modern browsers with ES6+ and acceptably in browsers without JavaScript. This approach is more sustainable for teams without the resources for extensive QA, and more beneficial to users of nonstandard browsers. Trying to recreate functionality that already works in modern browsers in IE11 is thankless work that is doomed to neglect.