The issue with preprepared demos is that you can carefully curate the scenario and make choices that you know are likely to show the best outcome, out of a wide range of possibilities. If you know your model (or VC product demo etc) performs poorly under certain conditions, you simply avoid them. This is a reason to be somewhat skeptical about demos.

No, the logic would be that a football player's 40 time doesn't impress, because you want to see the on field performance. Or a movie trailer doesn't impress, because it's only meant to get you to watch the movie which might be trash. A first date won't impress you, it will take multiple dates to understand and love a human.

etc.