I can't make heads or tails of the first sentence, must be reading it wrong.
But what I am saying is go play FO3, go get Power armor and get your DR to 60-80%. I don't know about you, but I get bored to death at this point because nothing can possibly kill you. And no, the lore never said "Power armor makes you Jesus Christ." If I recall correctly, power armor could stop small arms, but could still be penetrated by something like an AK-47. I also, again, do not see a purpose in making Light armor and Power armor function differently vs. the small arms. It'd be flavor only. All that would add is some immersion points, but a realistic impact on combat....? That fight was won regardless of if they both reduce damage to 20% or one of them reduces it to 10%. I wouldn't mind a difference for immersion points, but realistically speaking I don't see them bothering to dedicate time to such a feature with no realistic impact on gameplay.
I enjoy New Vegas more though because regardless of how strong I get, I can still feasibly die. This is not the case in FO3 because the armor you're allowed gets TOO good.
My point was that pure DR is both boring as hell to play with, and it has another issue in that it resists stupid amounts of explosive damage. Whereas your complaint is that DT only provides limited protection vs. larger weaponry (still helps, just not immensely), a counter complaint is that too much DR means a nuke can be set off directly under your feet and wtf you're alive. Aside from that, jesus it's boring. In New Vegas Deathclaws are something to worry about. In FO3? I would groan when I saw Deathclaws because it just meant I was about to waste stimpacks and ammo on them, not because I was realistically afraid of dying. The deathclaws are functionally identical in both games, it's the defense type that's different.
I also feel it's worth mentioning that J. Sawyer's mod eventually did what...? It stagnated armor. He nerfed how much HP you got from Endurance and HP per level, but Power armor got quite the increase. The end result was that the difficulty was functionally identical to how it was before....if you wore Power armor. Suddenly deathclaws on very hard difficulty hit you for only 150 per swing (compared to the ~280 in the vanilla game), but you only had about 170 HP instead of the 340 you'd normally have anyways. In the end, all this meant was armor stagnated and every character wore power armor. Very disappointing.
As I said, best solution is a mix of the two where DR only gets very limited amounts. Anything above 30% is absolutely pushing it. If you have power armor with 20% DR and 30 DT though, then yes that absolutely helps, because that's reducing a deathclaw's damage down to 90, which becomes 180 after very hard difficulty. Compare this to Light armor getting 20 DT and no DR, and the Light armor counterpart is taking 260 damage. This is a gap between the two that's very much noticeable, but also close enough that Light armor is completely viable. In practical terms it means that the Power armor guy can tank two full hits from a deathclaw whereas the Light armor guy can only tank one. However, you might prefer the added speed and crit bonus of Light armor and prefer to just avoid ever getting into a situation where you need to tank two deathclaw hits.
Alternatively, I would expand all armor types with perks. The system from New Vegas could more or less remain with very minimal DR in place for Power armor (10-15%) if they added perks that, for example, completely negated the x2 damage multiplier for headshots if wearing power armor and a power armor helmet. Meanwhile, award light armor some offense orientated perks (speed and crit) while Medium gets general utility. (modest DR bonuses, bonus to explosive resistance, bonus resistance to torso being crippled, that kind of stuff)