But setups get equally complicated, even with human software engineers. The approach that the OP is talking about applies only to experienced, good architect-level SWEs, and I suspect that the code quality and its problems are going to be the same whether they are directing LLMs vs a set of junior SWEs to write the code.

There is an inherent level of complexity in projects that solve some real world problem, due to all the code handling edge cases that were added incrementally over time.