That makes it a requirement as far as you are concerned, it would be for me
Seriously, I happen to agree with you if you haven't noticed. The reasons you bring out are practical points more than "emotional" points. I believe that it should be a requirement from a practical point of view not as an agency standards point of view. I see how the hoses get bent and stressed on non-rotating first stages. Rotating turrets are superior in this regard.
It's a requirement for me. I think a bottom port and rotating turret are objectively better.
But, there is such a wealth of collective experience with using regs of the ScubaPro Mk17 style successfully and safely that I don't feel like I could say it has to be mandatory for anyone diving backmount doubles.
One is better, but the other really is good enough, if that's what the diver wants.