Sure- the way I worded it was misleading. I didn't mean that the difference is 100 dps with the maxed power damage (pistol/smg power mag, power amp IV, maxed power passives), but that the difference between the two evo's, in themselves, is about 100 dps- and that, even with the maxed power build the damage difference still isn't that great, especially considering what you're giving up to get there (DR and increased priming duration from 6b, a mod slot on your gun, your Armor Bonus gear slot). And if you're using a big shotgun with Warp Ammo (as you should), then stuff like phantoms/collector captains/brutes/etc. aren't going to stay alive long enough for that extra 6a damage bump to matter anyways.
You're right, the damage difference isn't that great on its own, but that small difference multiplies itself for every stack of Reave you apply AND for every additional enemy you hit in your Reave radius. I understand what you're saying, and I agree - if you're using a big shotgun or other weapon damage build, Rank 6A doesn't make much sense. In fact, Rank 6A doesn't make much sense for any build, EXCEPT if you're going for an maxed Reave DOT-based build.
Well the first question is how much DPS do you lose by having no cover penetration whatsoever?
Secondly, how many Paladin shots are you saving by taking 6a instead of 6b?
For some perspective on dps, Hurricane will do ~ 5100 / 4140 barrier DPS on Justicar.
I actually lose very little DPS by using no cover penetration. I tend to prioritize enemies out of cover over enemies in cover anyway. Plus, if I want to hit something that's in cover, I can just use Pull or Reave on it to stagger it out of cover. With the Paladin's high damage per shot and Warp Ammo's armor weakening, I'm losing very little damage to armor DR. And the pistol piercing mod isn't going to give me enough penetration to double-hit anything anyway. The biggest thing I think I'm losing is the extra DPS I would get by using the extended mag. But I don't really care much about that, because emptying the 3-shot clip takes about the same amount of time as Reave's cooldown, which gives you a good rhythm when you're playing.
I don't get what you're trying to say with your second point.
Anyway, I never held this out to be an optimum high-DPS build. This is an "EZ-mode" build - it doesn't take a ton of skill to be extremely effective with it, even on Platinum. Also, DPS is limited by situation. A lot of stuff (including Phantoms and Dragoons) can be dead with this build before they even get in the Hurricane's effective range. No, it's never going to outperform a Hurricane (or any number of other weapons) right in a boss's face, but it will outperform a Hurricane when you're shooting at something (especially mooks) halfway across the map.