Putting a government monitored streaming video camera in every bedroom and bathroom in the country to detect sexual assault would also be "defense in depth". But it would be a terrible thing to do, both because it's easily evaded (do your rape someplace else) and because of the intrusion. Any kind of defense in depth argument has to consider how easily bypassed the defense is and the cost it comes at.
Believe it or not, most people don't play video games against strangers. Anti-cheat is not of any value to them. Even for people who do play video games against strangers even uncompromised anti-cheat doesn't stop many forms of cheating like macro-mouses. Especially now with all the success being shown at machine learning playing video games with nothing more than a video feed and the button inputs, the amount that anti-cheat can help is clearly quite bounded and getting worse over time.
And the cost? Anti-cheat comes at the cost of general purpose computing, at the cost of being able to control the computers with which you trust your most intimate secrets. It's a civil liberties nightmare, or at least a per-requisite technology for many such nightmares. Opposition to anti-cheat is opposition to RMS's Right to read dystopia (https://www.gnu.org/philosophy/right-to-read.en.html).
I don't think it's too far a leap that saying that anti-cheat or DRM technology that comes at the expense of the availability of general purpose computing is more of a problem for human rights than the farcical bedroom cameras I started with.
So when you advocate anti-cheating technology that locks users out of controlling their own computers, you're favoring an at-best incremental improvement which can still be evaded for a narrow application that most people don't care about... and this comes at the expense of imperiling the human rights of others.
Like with many things there is an asymmetry to the costs: Anti-cheat and DRM substantially fail if even a moderate amount of dedicated people still have a way to cheat. Yet the damage to people's freedom from the loss of general purpose computing is still substantial even when the lockdowns can be evaded.
If anti-cheat came at no meaningful cost the fact that it could be evaded wouldn't be a meaningful argument against it. But it's expensive to develop, intrusive, disruptive, and the more successful it is the more effective it'll be at being abused to deny people control of their computers in anti-social ways.