Don't you think that the reason so much of whats being discussed here is arguable is because the discussion morphed to where it revolves around "carry preference", rather than self-defense effectiveness?
It seems to me that as long as two people are simply "carrying their guns around" (one in C1, the other - C3) there is no PRACTICAL difference between the two. No need to use the gun?...no foul. Yet if presented with the identical self-defense situation the difference between the two becomes very apparent. That's the reason C1 is the "recommended method of carry.
Fortunatelly, the overwhelming majority of us will never experience an actual need to draw and fire, so how we carry won't ultimatelly matter. But for those "few" who DO have the need I suspect that those carrying C3 will probably wish they hadn't.
It's not a question of "right or wrong" but rather, optimal or less-than optimal.