Even if nobody is "cheating" your particular definition of cheating, the benchmarks are _somewhere_ in the super-structural gradient descent. Models are benchmark-maximising machines at some level, so I think the benchmarks are inherently a bit useless.

This is not really surprising, benchmarking _people_ doesn't work. You can only get a decent measure of someone's coding abilities by personally interacting with them. Given that models are basically person simulators it would be weird if benchmarks kept being useful as the simulation got more accurate.

I think what I've just said is basically just a more roundabout way of what you said: "Goodhart's law at work". It really is a law.