it's got nothing to do with ability (or competency) and everything to do with regulation.
I think it has
everything to do with competency. Why else would numerous regulators not permit captains to operate in the RHS without special training? I would suggest that an FO, trying to recover from a spin at night with a sidestick, would do a better job of it from his "normal" seat than the other. I certainly am less comfortable in the RHS.