Interesting points! Starting from a narrow perspective gives you feedback that is valuable, not noise that you can ignore. Most founders set their sights on an audience that is overfit (too narrow) or underfit (they have no experience). Striking a balance is key.
A marketer's perspective would be that the job of the ten words above the fold is to entice you to learn more, to pique your interest. Not at all to communicate everything about the product -- docs are for that. I don't think it's fair to say that these statements aren't "grounded in reality," but I do understand your sentiment.