I've had a very different experience than yours with the Typescript codebases I've encountered, which were mostly well designed.
I have no doubt codebases with polymorphic union type abominations exist, but I wouldn't say they are the majority, far from it in my experience.
It also seems to me those are a case of "problem lies between chair and keyboard", not a fault of the language. Bad code can be written in any language.
> I've had a very different experience than yours with the Typescript codebases I've encountered, which were mostly well designed.
Agreed. And in fact, the founders of a project having explicitly chosen TypeScript is often in and of itself an indicator that the team cares about code quality and writing style.
As you say, you can write poorly in any language. But people who care about quality choose TypeScript.
I have no doubt codebases with polymorphic union type abominations exist, but I wouldn't say they are the majority, far from it in my experience.
It also seems to me those are a case of "problem lies between chair and keyboard", not a fault of the language. Bad code can be written in any language.