Saying "surely, everybody does X" is a sure way to be wrong. You're even spectacularly failing at making your own point by acknowledging in the very same comment that there are, in fact, people not doing it. Some people are different from you, deal with it.
That being said, it's true than we can assume most of new software are generated. No need for hyperbole on that. An interesting fact is that it makes grandfather's concern moot: people who are generating their code don't care much if a dependency goes unmaintained, they can have it replaced by an other one in matter of minutes.
There's an other objection to openai-cli we could raise, though: why use a generalist developer tool, containing probably hundred of features we don't need, when we could make a bespoke specialized version, perfectly fit to us, in like 25 minutes? I can get that there are audiences where this would not even come to mind to the users, but we're talking about a developer tool, here. The value of that is questionable. And ironically, those who might from benefit it the most are those who don't want to generate their code.
they didn't say "surely everybody does" they said "safe to assume all", when really what they should have said is "safe to assume any" meaning any that you encounter and consider using.
I think it makes sense as a reasonable heuristic going forward, assume the MVP was vibe coded or nearly vibe coded (a weeks worth of human / agent work together, then initial release)
Considering that "it's safe to assume everybody does X" while perfectly knowing "there are actually many people who don't, but who cares" is honestly kind of militant conformism. You can expect it without assuming.
You put it better than me