That would help a little.
But I still feel that it’s pushing the work of getting the format just right onto the thousands of users who will use the form rather than doing it once, at the source.
But at least that’s better than forms that tell you after you’ve submitted that you made a “mistake”… but will only tell you one mistake at a time. So after you correct that and re-submit, then it tells you about the second form field that it’s not happy with.