The fact that he thinks DEX-based is 'significantly' weaker at dealing damage than STR builds shows that he hasn't done his homework. I have done the math, Bane of the Living is extremely competitive with even Vanquisher in most scenarios.
Of course you do come across monsters with immunity to negative energy but those aren't typical, and losing a bit of damage against those few mobs doesn't break the DEX build at all. In fact I rather think it adds an interesting level of depth to the character that one has to switch out one's weapon from time to time to beat up undead or similar creatures. But maybe that's just me, I guess to most people the idea of pressing a button in combat depending on the enemy type is just not 'optimal'.
Finally the idea that any enemy that's Evil, including Rovagug, will pose a threat to any build that optimizes even a little bit for Smite, is laughable - the bonuses are simply too good. Ok he will land a bit of damage due to his stupid unresistable spell damage, he's still going down, fast.