My arguments against splitting magical armor are that it cripples magical armor into uselessness because instead of needing to worry about keeping 1 bar in decent shape, you need to worry about balancing 4+ bars. In a game where 80% or more of the loot you get is RNG-based (drops & shops).
So now you need to rely on the RNG (in the limited resource/limited drop game) for an additional factor, in addition to all the other things we're already relying on the RNG to provide.
Your Elemental Armor idea is also redundant because this game already has Elemental Resistances. You could make an argument for replacing Elemental Resistances with your shields, but that would be inferior because resistances reduce damage even if you don't have magical armor.
The magical armor idea also doesn't take into account the makeup of enemies and the skills they use. If the enemies are varied and can use several different elemental types, then that makes your split magical armor even weaker. Even in the best case, where the enemies only use one elemental type, that still leads to you reloading and putting on all your best Element X gear. Each and every time.
Your idea does not add excitement or interest to the game, it adds a fresh layer of tedious micromanagement.
