The biggest problem with Typescript in the modern era is that LLMs are pretty bad at it, at least as compared to some other languages that are more well suited to LLM generation. What you say may have been a boon in the olden days, but it is hard to justify now. It is difficult to avoid Typescript/Javascript in the browser, sure, but now it's just as fast to duplicate everything in another language for the backend and at least gain the advantages on that end.