Well, dwarves miss a lot in general ... now sure, dwarven tanks are really tanky, but the longer combat lasts, the more pain the party cops ... thus offense is king.
There's been debates about offense vs. defense before, but shuffle around with different players in LFR and you'll notice offense outclassing defense.
Warforged get a feat that gives them +1 to hit if an ally is adjacent to the target.
In combination with brash strike and really high strength, warforged were churning out the pain.
Using a board for a bit more AC, granting CA is usually not an issue 'cos your foe is dead (and other players were deliberately provoking OAs from these marked enemies just so combat challenge proves fatal).
Minotaurs take a swing as they fall down .. that in itself is broke, as healing effects (such as *cough* consecrated ground) will get them conscious again.
In contrast, the dwarf I saw was seriously struggling, and got mobbed by a bunch of minions at one point .. where 2 or 3 points of extra hitroll (which is where it's at when talking about warforged) would mean cleave churns through them.
Sure, he held them off fine ... but other characters were taking some pain, the leader ran out of healing effects, etc.
Especially in LFR, where a party of level 1s can expect to take ongoing damage and other status effects, the only real way to be consistent is to make sure your enemies fall fast.