DRK did in fact get no love in 4.x, and it only makes it worse in that people keep saying stuff like "DRK is fine" when they really don't know what they're talking about. DRK's toolkit is greatly flawed compared to the other two tanks and makes up for it by being extremely situational, that being magical damage. DRK needs enemies to perform magical damage tank busters to be on par with the other two tanks, and while this happens more often then not, it does not always happen. That being said, it still falls short in DPS.
I wouldn't say not to bother entirely because there is the hope and chance that one day they actually give DRK some attention and care into having a strong identity of its own. For now, it's simply got the most undertuned ultimate CD, most undertuned -30% CD, the poorest passive mitigation, weakest self-healing, most boring rotation, and lowest DPS.
WAR has a better ultimate CD they can use every 3 minutes (literally on same CD timer as WHM's benediction) as opposed to DRK's 5 minutes, better self-healing, and higher DPS. DRK has a 10% HP shield it can give other players. While this is strong, it simply isn't *that* strong compared to what WAR brings when in the hands of a capable player. On par would be the closest you could argue.
As for PLD vs. DRK, that's just a joke. PLD is massively stronger than both tanks combined right now.
They've made this tier "viable" for all tanks by making the fights really easy in comparison to previous raids.