I guess I never thought about that because I have zero interest in maintaining a DPS set. My only interest is in achieving my tank set (which it seems we agree would be fastest under MS>OS for a tank).
So perhaps if you adjust your statement to “MS>OS favors people who multi-spec and raid as DPS” I would tend to agree. But again, I’m only concerned with gearing my one and only spec. My wife, a healer, is also only concerned with gearing her one and only spec with zero interest in a DPS Shadow off-spec gear set.
Anecdotally I’d say people who will actively multi-spec and care about maintaining multiple sets of gear are in the minority by a significant amount. But, if someone disagrees with that I wouldn’t have any data on hand to refute it.