I personally don't think the plate adds enough height to be an issue. So, for the idea of milling is better because it gets the optic lower, isn't worth milling alone, IMO. The MOS plate is not near as tall as other guns adapters. Even then, I wouldn't mill for that reason.
As for the milling creating a tighter pocket that is somehow better for the optic, I'm not sure I buy that. It may take stress off the screws, or at least some of the stress, but the internals of the otpic still take the same stress. The slide still slams back and forth.
If I was buying a new gun and that gun has the OR option, I'd choose that.
The ability to change otpics, take it off completely and shoot production, and resale make the OR a better option for me.