Apollo DomainOS (Aegis) was technically better than Unix.
At some point (before my time), marketing must've decided they needed to be more Unix-compatible, and they did some clever things to also give it multiple Unix personalities (both SysV and BSD), while still keeping their original better personality.
One place you'd feel pain around then, on most any Unix platform, is in downloading "portable" code off the Internet. Even for code already made portable in some sense, you'd probably have at least modify the Makefile, if not at least one C file, to select what portability you wanted, or to work around flaws in their portability. (SunOS 4 was my favorite for awhile, and at least half the reason was that code I'd grab from an FTP site was usually easy to get running, because it was probably developed on either SunOS or at least another BSD. Ultrix was also OK.)
As a teen, I managed a porting lab, so I got to sysadmin and own-time develop on all of them. Writing portable C code for the different Unix workstations, I'd have to do it in a subset of K&R C, plus a portability mechanism that I built as I went (for architecture differences, library differences, C compiler differences).
I do recall the Apollos being one of the more annoying Unix workstation platforms for C. I think they preferred safer languages for systems programming (again, they were ahead of their time), and maybe they didn't go all-in on developer ergonomics for C. Also, I guess the compiler probably predated ANSI C.