I doubt NetBSD "just works" fully on those systems either. I see a lot of rose tinted glasses when NetBSD portability comes up. Those older systems barely get stress tested, as the system has become too large to be self-hosted on them anymore and has to resort to using cross compilation to build a working base.

At least OpenBSD, when it says it supports a platform, _actually supports that platform_, and the system is stable enough that it can build itself.