I was doing some comparisons both yesterday (pre-patch) and today (after patch) between Ret and Frost DK. While Frost was slightly nerfed and Ret was slightly buffed, the difference from yesterday isn't all that noticeable. Both of these characters are wearing the exact same gear. Unfortunately, Recount doesn't seem to work atm, but my conclusion is this:
Ret: Templar's Verdict and Exorcism both crit around 40k while Crusader Strike and Judgement both crit around 20k.
Frost: Frost Strike crits around 40k and Obliterate crits around 75k.
a) I literally feel like I'm doing twice the DPS on the DK, though my rational side tells me the difference can't possibly be that huge. I hope to get Recount working soon.
b) Ret feels WAAAY more clunky and slower to play and you much more often find yourself waiting for an attack cooldown. Ret simply doesn't play as nicely.
c) While DKs must keep their diseases up, paladins also have to keep Inquisition up. It feels more resource demanding to keep Inquisition up compared to the disease appliers from DKs.
d) Frost also seems to scale better since Obliterate does some sickly 396% weapon dmg compared to the 260% (+ some minor damage) on Templar's Verdict. You can also use Obliterate way more often than Templar's Verdict.
e) With Killing Machine on the DK, I'm critting all the fricking time. So even though paladins got a crit buff on Inquisition this patch, Killing Machine is just soooo superior it's insane. I feel like I have at least a 50% crit chance on average on Frost Strike and Obliterate due to this skill.
f) DKs can enjoy a lower GCD as well.
I know MoP is still far from being released, but I don't know what Blizzard is smoking if they think these two classes are anywhere near each other in performance. I cringe every time I switch from a Frost DK to a Ret pally.
What could be done? Well, I think Templar's Verdict needs to hit harder, and either the seals or inquisition (or both!) could be improved. Something also needs to be done to make gameplay feel smoother and more enjoyable on the paladin. Like I said earlier, Ret feels extremely clunky, slow and boring compared to Frost.