I've come to the conclusion that they know a lot, but they're not very smart. Not even the best ones.

They know far more than any human ever could: they've read all the books. Their knowledge is enormous. And that often includes how to apply it in standard ways, and sometimes in slightly non-standard ways. But whenever something gets complex, detailed and nuanced, they can't keep up with a human. It becomes a shallow illusion that's easily punctured by just a bit of critical thought.

You mention system architecture, but even for writing code, the code it writes is often horrible. It makes it work because it has a feedback loop that rapidly tests it and ensures it will work, but the actual code it writes down is often not something I would feel comfortable showing to another programmer.