OpenBSD (and most other BSDs) are willing to make changes that break binary backwards compatibility, because they maintain and ship both the kernel and userland together as a release and can thus "steer the whole ship", rather than the kernel being it's own separate component developed like with Linux.
Sure, that's usually true, but Debian also has that ability in this case ( they can fix, patch, or update everything in the repository). The issue is mostly with all software that isn't part of the distribution and the official repositories. Which is a lot of software especially for Debian. OpenBSD doesn't have that issue, breaking the ABI won't cause tens of thousands of user applications to break.
But I agree that Debian is still too slow to move forward with critical changes even with that in mind. I just don't think that OpenBSD is the best comparison point.
