True. But Apple, with such a focus on UX, cannot reasonably afford more than ~200 millisec when checking a password; and still it scales linearly, so the solution for concerned users still involves creating a more complex password. Doubling the amount of time it takes to hash a password will have the same effect as adding 1 more bit of entropy to the password, which can easily be beaten by adding a single character to it.

If you consider caching of keys, there's no reason that the first login attempt after a cold boot couldn't take 1-2s. Each subsequent login would be roughly instant.