Damage treshold takes damage away equally to the DT rating, meaning an anttack that does 40 damage against a DT 5 would do 35 damage, which would relly give a bigger difference comparing light and heavy armor. Max DT of light armor could be 10? Heavy armor maybe 18? you must note that the best weapon at best skill level does about 30 damage.
well, it's actually "damage = (attack-DT) * ((100-DR)/100), I think.
Glass should be higher than most heavy armor, though. Hypothetically, steel will block damage up to a point, and once you exceed that, it still slows down the blow as the weapon penetrates. Glass... you pretty much want that to stop almost everything right up until it shatters. High DT, low, possibly negative DR (so if you take damage, shards of your armor hurt you as well as the blow), and one of the lowest durabilities in the game.
On the other side of the coin, you could make Daedric have a slightly lower DT than Ebony, but the highest DR in the game. Leather, on the other hand, would have a very low DT, but a modest DR.
DT and DR don't really make for an interesting armor system unless used together
Do I want to stop all damage from mudcrabs, or am I interested in taking less damage from the heaviest hits? It blurs the progression... and if we can blur whether light/medium/heavy is the bet option for a character moment to moment, why not do that too?