I'm left handed, but use my right eye. I see better with it but that's not the reason, its just that it feels right with my right eye. I do several things with my right hand or that are right handed methods. I think it's not uncommon. I can not write with my right hand and cannot eat righthanded. I also shoot my rifle right handed using my right eye and can bat at baseball right or left handed equally well.
I had bought the optional high relief eye piece for my 5D MK II, and then a hooded eyepiece for my 5D MK IV. I was disappointed that the hood does not work with mirrorless, it kept stray light from distracting me when using the viewfinder. I also had a rear LCD pop up shroud that let me have some use of the rear LCD outdoors during the day. There is a shroud for the mirrorless cameras that Velcro's around the LCD but needs it to be folded out. I haven't bought one even though they are cheap. The R5 viewfinder is much better for me in daylight than my R is.