This has nothing to do with there being a healthy market of operating systems to choose from.
> I’ve seen the fragmentation in edge devices
How many versions and patch levels of Windows exist? How many are currently deployed? How many must stay on the current version because of fragmentation?
> You know how many bugs you have with one stack?
The scenario that started this discussion is a single bug in a single piece of software impacting a large number of businesses, some of which are safety and life critical, all of which are on a single OS.
It's not a question of "how many bugs," because you can't fully eliminate them in any system which is actually updated _ever_, it's a question of "how many people does this single bug impact?"
Will this require more time and labor? Yes, of course. Does that make it "absurd" to consider? No, that's pure hyperbole.