My suggestion, Netherite and Diamond Armor should have less Melee Protection.
But here's the catch. You can put Chainmail armor underneath any other armor, making the Melee Protection max out.
I think this would be a really good addition to Minecraft and still fit Minecraft as a theme, because thats how Chainmail was used in real life.
This could also open the door to stackable Elytra/Chestplates.
Dosent fit the topic, but I think it would be cool to be able to craft totems onto shields.