A suggestion to add greater differentiation between armours, and between light, medium and heavy armour in general:
Add resistance to a specific physical damage type to all armours based on quality level.
For example, all/most light armours have resistance X to one of Bludgeoning, Slashing or Piercing, all/most medium armours have resistance X to two of the same, and Heavy armours have resistance X to all three.
Where X is something like 0/2/3/4/5 for Poor/Normal/Expert/Master/Legendary armours.
As examples:
Padded Clothing: 2 resistance against Bludgeoning
Expert Chain Shirt: 3 resistance against Piercing
Master Breastplate: 4 resistance against Slashing and Piercing
Legendary Full Plate: 5 resistance against Bludgeoning, Slashing and Piercing.
You could also have traits like thermal, which would apply the resistance to an element - possibly with an equivalent penalty to the inverse type.
This might allow low level players to have more interaction with the resistance/weakness rules. Not only because they'd now be on the receiving end - and the GM can interact more with it, but also because it would provide thematic explanation for things like a small fire weakness on a Guard at a hilltop fort, or even just archers on a wall with a small piercing resistance.
It would also make armour do some of what I expected armour to do when I first encountered D&D — reduce damage. AC feels like your heavy armour is helping you dodge. Now I'm familiar with it, it feels normal, and I can see the thematic arguments for it — the blow bounced off the armour, or failed to puncture it. But as a newbie to D&D it certainly felt odd.
In practice this might be too much to remember if it was applied to all armours. So might work better as just an additional trait that can be applied to differentiate armours — certainly the game seems to be lacking interesting armour traits at the moment.
Damage might need to be increased slightly as a result, though I'm imagining most level 1 mobs will have poor equipment, and except against heavy armour, slightly more thought/planning by the players would avoid the problem.