I agree that you need both. But in my experience you need far fewer unit tests in a typed language in practice to be reasonably confident of correctness. Like, maybe 1/3 of the number of tests. The reason you need so many tests in JS is that its just so easy to accidentally refer to a variable that doesn’t exist anymore or something like that. And the only real way to be safe from that sort of mistake is to go overboard with unit tests and aim for 100% coverage, which destroys velocity.

As you say, unit tests and type systems are good for different things. Unit tests can be used as a poor mans type system, but that seems like an amateurish deal now we have typescript & friends. Well, at least for code you want to maintain long term.