I'm sorry you are stuck still supporting IE11. You could use an AMD loader and use imports in Typescript configured to transpile AMD modules. Most AMD loaders were tiny. The benefit to AMD modules in your case is that they don't need webpack to bundle, the (hideous) module format was designed to be bundled by raw concatenation and the Typescript compiler will still even do that for you with the --outFile parameter (or "outFile" tsconfig.json setting).

It feels like terrible advice to give someone, given ESM is far superior to AMD, and this would be going backwards in time, but in your case you are already blighted by the disease and it is advice that might staunch some of the bleeding.