These things are kind of orthogonal. OpenBSD maybe gets there eventually.

OpenBSD is like a very hardened safe, made of steel and huge bolts and locks. Very polished, very smooth and hard surface.

MAC/RBAC is like having security officers, interviews, checking of IDs, filling in forms and getting an OK from ones boss before performing work someplace in the building and so on.

Both these things can be good. But OpenBSD was always about making a small system as hardened as possible. Evidently, they aren't completely done yet with making the core as hardened as possible.

Windows has great architecture, but lacks instead severerly this hardness which OpenBSD possesses. What use is MAC/RBAC if someone can gain kernel access with a 0 day exploit?