If you look at both PLD and DRK:
Rampart - Shadowskin
Sentinel - Shadow Wall (10% difference but serves its purpose of breaking a tank buster)
Bulwark (Physical) - Dark Mind (Magic)
PLD Shield - Dark Dance
Hallowed Ground - Living Dead
RoH STR Down - PS INT Down
Some of my Paladin friends aren't to excited about Sheltron so I left it out, I guess it's very hard to time and ends up eating an auto attack instead of what you really want to block, like if you are solo tanking Rav Ex and want to block the split-able tank buster solo and you time it wrong so it takes an auto and then you eat the full buster.
Taking into consideration Dark Dance's effect with Dark Arts and the 33% up-time on the buff, assuming you keep it on CD for an entire fight, and assuming an average Paladin block rate/strength, a shield and DA/Dark Arts actually equate to roughly the same overall damage reduction, as long as we are assuming auto attacks, which regardless of what you're doing can be dodged/blocked. Now there are certain mechanics, typically Tank Busters that can't be dodged but can be blocked, but more often than not you don't want to leave stopping a tank buster up to the chance of if or if you won't block. The proposed change to Dark Dance would severely handicap this concept dropping its overall effectiveness by around 15%. Now if you want to boost the parry to 50% and increase the amount of damage parried by 20% if you use Dark Arts, that would make it equally effective and eliminate the dodge.
I think since these classes are all designed in a vacuum they all have paper balancing factors and while on paper DA/Dark Dance is roughly the same DR over the course of a fight as having a shield, it just doesn't seem like it because RNG mitigation is never good mitigation.
From the list above it looks like PLD is more niche for physical and DRK is more niche for magic, yet they can both do either it's just one will be better than the other in certain situations. Since DRK was designed along with the new content it's a very safe assumption we'll see a need for magic damage reduction meaning DRK will shine.
The only real change I want is more group utility. Delirium Blade is great for the -10% INT which was amazing in T13 with a Monk, and since no one in my FC is leveling Monk for HW DRK can bring that debuff. Looking at PLD though they get -STR% on Rage, they can Stoneskin, Clemency, and Divine Veil which are all awesome utility. I guess Clemency is really only good for downtimes in combat because while casting you can't block or parry so a chunk of your mitigation disappears to cast a heal.
I would like Delirium to have an extra effect, like Magic Vuln increase to help your casters, possibly add an effect to Dark Side that changes your damage to magic so you can benefit from your own debuff. It fits with the ability thematically. Make Sole Survivor cast-able on a party member, if they would drop below 1 HP, instead stop them at 1 HP make them "zombie" that is immune to damage for 5s and heals you for 20% of your HP and MP, it would still work on a MOB as well, but obviously not the immune to damage part, just the 20% HP/HP if they die with it. I guess I do hate self healing effects on a tank so if Souleatter would instead of a health buffer based on damage, that would be much better.