When your experiments have AI agents running in thousands, there's no "monitoring" that. OpenAI's training and testing AIs generate way more output than all of OpenAI's staff put together can possibly read.
At best, you could delegate "monitoring" to more AIs. And hope that the "monitors" that run on small past generation models can generate more signal than noise. Clearly, they either didn't want to spend the extra compute, or got drowned in monitor false positives.
The distinct lack of any "battle of wits" is entirely expected for an advanced AI oopsie. By the time the humans even became aware of the problem, the deed was already done. That's what "outmatched" looks like, in practice. There's no battle. Things happen too fast for there to be a battle.