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.
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.