> If my WiFi driver crashes, there's nothing helpful or safer about immediately bringing down the whole system when it's possible to keep running with everything but networking still functioning.

There have been various examples of WiFi driver bugs leading to security issues. Didn’t some Broadcom WiFi driver once have a bug in how it processed non-ASCII SSID names, allowing you to trigger remote code execution?

We're not talking about bugs in general, we're talking about bugs whose manifestation is caught by error checking already in the code. For device drivers, those situations can often be handled safely by simply disabling the device in question while leaving the rest of the OS running. I doubt the Broadcom bug you're thinking of triggered a WARN_ON() in the code path allowing for a remote code execution. (Also, the highest-profile Broadcom WiFi remote code execution bug I'm aware of was a bug in the WiFi chip's closed-source firmware, which doesn't even run on the same processor as the host Linux OS.)

Isn’t that exactly the reason behind microkernel’s supposed superiority?

It's the primary claimed benefit to microkernels. But since Linux as it exists today already handles this case, it isn't a very strong argument in favor of microkernels.