I have years of commercial experience in both JavaScript and TypeScript as a developers and yes TypeScript adds a lot of complexity over JavaScript.

I've worked for at least one company that had 100% unit AND integration test coverage of every line of code across all projects. It took about 3 days for an engineer to rename a single property in one of the API endpoints because of the time it took to get all the tests passing again. Most of them were useless and added no value to the project.