I don't dispute that OpenBSD is good at the small-bore Unix stuff. They are! I think OpenBSD is the undisputed master of small-bore Unix security. If you want something in userland priv-separated or some ID randomized, call the OpenBSD team.
The problem though is exactly what this article says it is: the code OpenBSD has custody over is a small fraction of the code users need to run, and OpenBSD's code just isn't up to the challenge of securing other people's code. Modern Linux security has taken the other road: part of the kernel's job is --- at least in GRsecurity-world --- to assume that you're running insecure C code, and still not lose your kernel to an attacker's persistence tools.