Does he have some custom build network router that he trust? Putting tape over your camera means you know enough to not trust the laptop hardware neither the OS or browsers like you said.

But he says: "We use .. Sonos system with Spotify for music, a Samsung TV, a Nest cam for Max". So all of his appliances do get outside. I did a double-take on Nest cam. So he's streaming videos from his house on the internet with a closed source hw and software.

I didn't read the part about Nest to be fair but with some basic network design you can easily segregate networks and reduce your attack surface massively, even if you're using internet connected devices (seperate vlans, use http proxies with ACLs, no inter device communication where not needed).

The difference between a switch and a laptop is that your switch isn't running browsers with 0days found regularly, no malicious JS payloads, no phishing emails.

To exploit a switch you generally need access to the management interface, something anyone who has any experience with networking does not put on the same network (virtual or physical) as laptops, iPads, televisions, or internet connected cameras.

I agree with what you are saying, however tape over the camera means you don't trust the OS or the hardware manufacturer with a console command like modprobe to actually do it's thing and disable the web camera.