In today's massive applications, the number of people who can see the entire structure is very limited—yet commercial applications still work.

And I think GPT Codex and the products from AI companies are, at least for now, working reasonably well.

Of course, it depends on your baseline for quality.

But here's what I think is the core point:

Modern SaaS applications have become significantly more complex compared to older codebases. If you look at old books on open source architecture, the lines of code and overall size were much smaller. But today's commercial applications require a much higher level of complexity just to be marketable. In that kind of complexity, there are bound to be many bugs. But I think AI has significantly reduced that complexity burden