It sounds like you're making the mistake of thinking that TDD means writing the tests first. That's not quite right but it's understandable that lots of people believe it given the way TDD is usually discussed.

In TDD you should be writing one test first. Then you write enough code to make that test pass. Then add a second test. Get that to pass. And so on. If you realise you missed something you can delete tests that don't make sense any morejuat like you delete code that doesn't make sense. In essence TDD is about writing the tests in parallel to writing the code instead of writing them afterwards.

You can easily prototype and experiment with TDD because you're never much further ahead with your tests.

TDD is faster than writing tests later because your code has to be testable throughout the process. Writing tests later often means you need to refactor or rebuild to make it testable, which is a waste of effort, even in a prototype.