What would qualify as proof? If somebody builds a good product and ships it it will just look like a good product. People will call it vibe coded slop when it fails spectacularly.
If there isn't a strong uptick in the general quality and usefulness of software within the next couple of years, then it's not clear what AI coding/design is actually buying us. Other than possibly some cost reduction, but it would be optimistic to assume that the savings go to the users and not to big tech. Regardless, the proof will be in the pudding.
I mean they would provide it--you would think this is something the AI coding businesses would be highlighting. "Here's an app tends of thousands use every day built with our AI tools!"
Heck they did it with languages for the longest time. Here's twitter, we built it on Rails, everyone use Rails! Facebook, built on PHP, everyone use PHP! Feels weird that if these AI tools are doing all this work that no one is showing it off.