Redundancy is a good thing. Go look it up in a dictionary.
There is a reason people have two kidneys. What if a hypothetical human designer had said: 'No, two kidneys, two eyes, a bivalve heart, two lungs.. all that is redundant. One of each and a simpler heart will do.'
Because skills tend to get used up, and they need to share the load?
What?
My problem with medium armor is just the definition of medium armor is not clear.
In D&D it sort of makes sense, as leather and padded (sometimes chain) is considered light, ringmail, scalemail is considered medium, plate and full-plate is considered heavy.
Now in TES it works differently mainly differentiating it with the material they're made of. Problem is if Orcish is medium why is Ebony heavy? If chitin is light, why is dreugh medium? If bonemold is medium, why is glass light?
The borders between the two are slim at best.