HW DA usage:
ST > CNS or Soul Eater. oGCD Flat potency.
AoE > Abyssal Drain. oGCD Flat potency and small heal.
SB DA usage:
ST > Syphon, CNS, Soul Eater. oGCD Flat potency.
AoE > Abyssal Drain. oGCD Flat potency and small heal.
ShB "DA" usage:
ST > Edge. oGCD Flat potency.
AoE > Flood. oGCD Flat potency.
What DA was in HW was effectively a oGCD potency boost via augmentation. What DA was in SB was effectively a oGCD potency boost via augmentation. What Edge/Flood is in ShB is effectively a oGCD potency attack.
What changed? Soul Eater is still the primary combo that you press DA/Edge in between. Delirium the combo ender and scourge became a simple high potency attack that doesn't interrupt combos(Blood Spiller), having virtually the same frequency to pad out the Soul Eater monotony. Power Slash didn't exist then and it doesn't exist now without taking over our hotbar space. Healing got removed from Warrior as well since their Steel Cyclone is just potency. This was a global tank design decision to remove both tank's AoE tanking edge over PLD via burst healing.
All that has happened is DRK turned it's 140 pot boost into a 500 pot attack with more flexibility in it's placement per minute. They removed the spam by halving the uses but more than doubling the power. DRKs Mana space by contrast is much larger allowing more pooling into buff windows.
The only real gameplay mechanic that was lost was the TBN MP > Blood play and that has no relation to DA.
DA as a mechanic of turning MP into damage still fundamentally exists. Just not spammy, has a different name, becomes an attack itself instead of a buff, doesn't have additional and often neglected uses like buffing a defensive cooldown that is essentially free now, and doesn't have a requirement of buffing an additional oGCD attack(CnS/DP) since those attacks just became seperate full effect oGCDs (CnS/AD respectively) making Double Weaving much less of a requirement.