The main benefit of YC startups is not that they have 10x engineers but rather that they are starting from scratch; hence, the AI works well in a greenfield project. Enterprise customers are a totally different ball game. Ninety percent is legacy critical code, and some decisions are not made to optimize the dev time.

Also, for Y Combinator startup, let say that the AI introduces a bug. Since there are no customers, no one cares. Now imagine the same AI introduces a bug in the flight reservation system that was written 20 years ago.