As far as I know that only tells you why it might have had to be Dallas at some point when regional centers made sense. Which changed somewhere around Paypal if not earlier.

I'm not saying that Dallas (or any other city) can't have some, even quite successful, startups. Just that you can't really compete being say "the third to fifth best choice for startups". At that point you're competing with too(!) many different cities. You have to be the obvious choice in a few, preferably large, categories; capture a lot of local talent (which is harder in the US), and most likely both.