> you don’t have to write the non-helpful types

This entirely depends on your tsconfig setup. You can run a JSDoc-typed project in strict mode exactly the same way you would a *.ts-typed project.

Do you know if it's possible to do that the other way around?

	▲	culi a day ago \| parent [-]
		You mean a TypeScript project without strict mode? Sure. Again, whether you're defining types in JSDoc comments or in .ts files, the behavior is entirely governed by a tsconfig file