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I agree that it's Acceptable Breaks from Reality as you mention. If you do have overly complicated piecemeal armor in a tabletop game, it'd be Misaimed "Realism", because it's a huge amount of not-fun work for the players, whereas in a video game the computer can handle all of the number crunching and random number generation ("dice rolls") instantly.
Inexplicable Treasure Chests seems related. Inexplicable Full Suits Of Armor in the treasure chests?
I don't see anything else more specific than that.
It does seem tropeable... Compare One Size Fits All and Set Bonus. Contrast Rainbow Pimp Gear. Becomes moot with Informed Equipment.
Is there a trope for how in most editions of Dungeons & Dragons (and, by extension, Pathfinder) suits of armor are usually treated like onesies (i.e the whole suit is treated as a single unit, rather than each piece having its own stats like in Video Games?) The main reason being that it's just easier than calculating the entire armor bonus from all the pieces, especially if a character is wearing mixed types of armor, as well as both games lacking Subsystem Damage. Pathfinder does have a variant called piecemeal armor,
and it's just as complicated as you would think. Anyway, I was thinking of putting it under Acceptable Breaks from Reality, but that's more of an index than a trope unto itself. I'm also not sure if most tabletop RPGS are like this, as I've only played a few.
Edited by Bootlebat