I've read through quite a bit of the comments here and am excited to see that this is current and being discussed.
Please allow me to offer my 2 cents.
I think that its fairly important to keep some DR perks for the simple reason that the Weapons and particularly the "shotgun class" weapons are not going to handle a complete shift to DT.
Background on Shotguns (not that you dont know but going to explain it anyway)
Damage, done per pellet of shot. Means ussually a shot is actually 7 smaller damage shots.
7x8 <means 7 shots 8 damage each.
Well with DT (damage threshold) we basically deduct the DT from the damage and we have the amount that gets through.
Lets look at basic Raider Armor, it has DT of 4.
The Damage for our shotgun becomes
7X4 thats 7 shots at 4 damage each.
Against Vault Security Armor, DT 8
7x0 thats 7 shots no damage. With the exception that there is always a minimum bleedthrough I think its about 20%
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I know this is not a popular go to example but if the Fo3 perks all become DT we should expect to see other weapons start to lose their effectiveness and the gameplay to lose its appeal as it becomes too easy.
My thinking is that if I can pick up Megaton perk with DT and Oasis Perk with DT then I quickly can have a whole lot of DT by around level 12. With Toughness thrown into the lot I might think that with that shift a DT of 12 with no armor would be possible with just 4 perks...
That is if the perks changed to DT.
Megaton Perk - 3 DT (seems small right?)
Barkskin- 3 DT (also seems small)
Toughness Rank 1- 3 DT
Toughness Rank 2- 3 DT
So thats 12 DT...Useing Metal armor which is feasible by this time that means I have another 12 DT for a total of 24...Rendering all shotguns ineffective and a whole large segment of pistol class weapons as well.
Examples of pistols that are ineffective
9mm, 10mm, 22, 9mm submachine gun,
just a few Im sure there are many more.