It's much easier to tell if athletes are doping than to 'detect' AI in text that's already Oscar-for-writing level good. I would suggest the latter is quite literally impossible.
> I have always heard that dopers are consistently ahead of testing regimes
I don't know about that, even the very biggest names with the most funding quite often get dinged for it. I suppose I'm not really saying that the detection rate for doping is high, though, just that it's much higher than AI detection in high-quality content (which I would suggest is approximately zero).