So you save a few milliseconds if you don't initialize some filesystems, good but makes very little difference in the end.
Not having a hard disk? Doesn't require a microkernel at all. Booting over LAN has been practical for a long time.
If I glance the closest linux machine I have, it has a 6MB kernel with 10MB initrd. To put that on a server with gigabytes of ram? Trimming an unused networking stack here is not the use case where a microkernel will help performance.
The "few milliseconds" was a response to "Your system will start faster because it doesn't have to do things like initialize the various pseudo-filesystems Linux has, or initialize the virtual file system, or any number of other tasks." Doing that init takes very little time and zero disk accesses. That and a few megabytes of ram are all you save by using a microkernel instead of linux in this situation.
Linux won't access the hard drive if it's unnecessary, same as the microkernel.
Not having a hard disk? Doesn't require a microkernel at all. Booting over LAN has been practical for a long time.
If I glance the closest linux machine I have, it has a 6MB kernel with 10MB initrd. To put that on a server with gigabytes of ram? Trimming an unused networking stack here is not the use case where a microkernel will help performance.