That's the point. If it is detectable, it'll get downranked for being low-quality.
Of course, this suggests a corollary: that Google shouldn’t be indexing the output of content farms where the writing and derivative-ness is strictly worse than what you’d get from an AI article generator. :)
... Let's start with some demonstrations of good AI-generated content being down-sampled by this policy.
Mission. Fucking. Accomplished.