I've subjectively detected this in previous codex releases where the 2 days before release of a new model the agent went from great to me pulling my hair out yelling at it. I think it's just a win-win for them. They need to ramp up basic capacity and usage on the new model, what better way to free up capacity than to reduce the effort with the current gen. There's not deep detectors that they've regressed (especially before this guy showed solid data).