Well here are a few questions.
Why are we okay with having multiple weapons with no or little mechanical differences but are troubled or hesitant to do the same with armor?
If the mundane damage types (bludgeoning, piercing, slashing) only matter when adding adding variants, named items, or modules to the game, couldn't this be the thought pattern for armors?
What if there were a simple variant rule for materials and armor? There could be multiple "top rank" armors but the armors would have different materials.
Fore example Studded Leather, Thick Padded, and Gladiator Plate could be the top light armor. All three offer AC equal to 12+Dex Modifier. However they are made of Leather, Cloth, and Steel respectively.
As an reaction or when taking the Dodge action (in 5e), a character proficient in their armor can give themselves resistance to a few damage type until the end of their next turn. In other editions, you'd get similar resistances by doing something.
The different material types would give warriors a choice of armor beside the gold cost.
Do you choose leather armor to dodge fire and lightning or wear metal to resist slashing and piercing? Or is resisting sonic/thunder and bludgeoning your jam and you choose cloth armor?