While the picture painted here is viceral... I think the reality is closer to this..

Before AI, most big software was desgined and originally writen by a few key (founder-esq) architects. But they can only add functionality at human speed, so the team grows, and the quality of engineer drops as the functionality footprint grows. Eventually the functionality is much bigger, but most of it was written by a much lower quality engineer, and thus the code (even if functionally correct) is less efficient and less clean, and the big refactors a talented architect would have done never happened, so it just got bigger and bigger and more unweildy and bug prone and inflexible - until some new talented architects see the waste and build a startup to displace it.

With AI, big software can be entirely written by 1-3 people, plus alot of agent usage. Which means it can be refactored more, and the design kept cleaner. But this only happens if those senior architects are actually paying attention and controlling the design. If the agents are heavily automated and subtasaking and controlling the design, then nothing much changed, because the agents themselves are no better than the "stackoverflow engineer".