I don't understand what the tsconfig has to do with understanding the source? Maybe when using different path resolving or different tsconfigs to compile test files vs. production files?

Many toolings make it so you don't even need to worry about the tsconfig anymore (though in reality it is very helpful to understand it).

To avoid breaking existing source bases, many features or corrections across the language versions are opt-in, so in some projects it looks like GHC feature pragmas.

This does not align with my experience of writing Typescript at multiple companies of varying sizes and open source projects.

Lucky you for not having devs that would rather be using Haskell Lens and stuff like that.