It would be cool if mobs dropped armor with (bonus attributes)[https://minecraft.gamepedia.com/Attribute] instead of just better and better enchants.
For example, you could have a pair of boots that makes you move quicker, but provide less armor. Or a chestplate that provides an extra heart or two but doesn't provide as much armor. Just as a couple examples.
Alternatively armor pieces or tools that apply a potion effect when equipped or in your hand. A pickaxe that applies haste when in your main hand for example (Not that it matters with Efficiency 10, but you get the idea).