Short version: I think we need a bonus to incentivize different armour types. I think a version of armour sets could work here.
One thing I realised as I played through the game is that if you have the equip load for it, heavier armour is always better.
It’s true that you need to spend points in equip load if you don’t like the heavy weight, but generally, leather is better than cloth and so on. To some extent this works, but I think it should be more like it depends on the build you’re going for.
So my basic thought is that we already have armour sets, like the Mariner’s set, the thieving drifter set, etc. It would be cool if wearing an armour set together had some kind of bonus related to the name and style of the armour. No need to alter anything else; this would work like you can have all the usual gems or enchantments on top of the set bonus. Ideally we would have bonuses that incentivize things like an int character to wear cloth or a dex character to wear leather, and also perhaps this would create some interesting builds. Obvious things are bonuses to particular damage types or to stamina/focus usage, but some more interesting ideas might be to alter how runes function, like say… the sailor set might change ice to make it push enemies back instead of freezing them or something (like instead of cold you’re attacking with water).