You don’t necessarily need to detect the cheat itself, you can look at things like players having suddenly higher kill rates and put them into a queue for observation by either more advanced (more expensive) automation to look for cheating or eventually involve a human in the loop.

That's true, if the player suddenly has higher kill rates. However, that doesn't work if they've been using the cheat from the start on that account. A sufficiently advanced AI powered aim bot would also be nearly indistinguishable from a professional player. Kind of similar to how Google created the CAPTCHA that uses mouse movement ... but had to go back to (at least in some cases) the additional old school captcha.