Brooks’s law was about humans, but the spirit still applies: the real bottleneck is how much of the system a human can keep in their head at once. Most agent setups I’ve seen don’t reduce that load, they increase it: more surface area, more glue code, more boilerplate that nobody fully understands.
The only places they’ve worked well for me are roles where you can afford to throw away 80% of the output (migrations, test stubs, scaffolding) and keep a tight human-owned core. Treat agents like interns you fire every night, not teammates you trust with the architecture.