Windows 95 & 98 would crash pretty frequently. Not as badly as win 3 though.
NT 4.0 was no bastion of stability either. Windows didn't stabilize until well after Win2000 versions.
MacOS 7 & 8 also not great. The first versions of OS X were also pretty flaky.
In my experience dependable reliability of workstations and servers didn't happen until the mid-2000s
where just software couldn't simply blue screen an OS, or lock it up forever.
If I remember rightly it was about that time that MS got serious about driver reliability, which seemed to
help a lot.
The middle versions seem to be the best ones somehow. Sire, the cooperative multitasking model of Mac OS 9 was a bit, crappy, but it was really reliable if you went to work at it from a task-oriented perspective. Same for Windows 2000, more stable than Windows XP for some reason.
For Mac OS X it was 10.3 to 10.5 that was the (seemingly) most stable.
I think the scope and size of hardware, software and interaction has just gone so large that it's not commercially viable anymore to test or QA the entire system to the same standard. It's also why service managers came along, we just assume that everything breaks and hope restarting it makes it go away...
My recollection of (Apple's) System 7 is that it really got bitten by the rise of programs running dynamic code (i.e. Netscape). When everyone was operating on relatively pre-vetted apps, which had their buffer overflows cleaned up, it played pretty nice, but when that wasn't the case, it really blew up.
System 7.5 was rather worse-off than 7.0, but it got absolutely slammed because it was the first major mac OS that got saddled with web browsing, and the OS was just not fit to handle apps that had buffer overflows.
That was the big thing about those mac OSes; since they had no memory protection, if any app on the system buffer overflowed, it'd crash everything. It was fine in an environment where you really were only running one or two apps that were known to be really rock-solid, but it wasn't able to police misbehaving apps.
Maybe they're not talking about the currently surviving mainstream consumer OSes? There were other contenders that weren't for consumers or didn't survive MS's bullying, and on the other end there's probably a reason mainframes are still in use in places.
The context here is desktop systems, not mainframes.
Though the interesting takeaway from your comparison is the fact that desktops these days run server kernels, which is a testament to the build quality of servers.
Which segues nicely into a recap of my point: 90s desktop systems didn't have memory protection et al so one buggy application would cause the system to crash. Everything was carefully layered like a house of cards. The switch to NT and UNIX largely fixed most of those issues but later builds of macOS seem as buggy to me as Win 9x and MacOS 8 and 9 were.
You're conflating workstations with personal computers.
In the 90s systems like OS/2 and NeXT were defined as "workstations" to make a distinction between the old lineage of personal computing platforms (like Win 9x and Mac OS running on typically budget hardware) from high end systems running typically multi-user systems (often literally mainframe OSs).
Post-90s and the "workstation" definition went away when NeXT became OS X and NT replaced the DOS-bootloaded Windows lineage; and dedicated workstation hardware became cost ineffective due to improvements in consumer hardware -- not least of all x86 (and later AMD64).
Windows 95 & 98 would crash pretty frequently. Not as badly as win 3 though. NT 4.0 was no bastion of stability either. Windows didn't stabilize until well after Win2000 versions.
MacOS 7 & 8 also not great. The first versions of OS X were also pretty flaky.
In my experience dependable reliability of workstations and servers didn't happen until the mid-2000s where just software couldn't simply blue screen an OS, or lock it up forever.
If I remember rightly it was about that time that MS got serious about driver reliability, which seemed to help a lot.