I know that during the design of the original Pixel laptop, things like physically powering down and disabling the camera, rather than doing it in firmware was important to the team at Google. I wonder if they have maintained that vigilance.
One presumably pays money for a device with Google's name on it through which all of your network traffic flows, and you're worried about a microphone?
(I well and fully get your point, I'm just amused that, in the bigger scheme of things, a microphone is the problem here.)
People care more about their physical privacy than digital, as they should be. Google snooping on my packets is less intrusive than a camera or microphone in your home, looking/listening at you.