CB is good, but it isn't everything. The closer to 100%, the better, of course, but from a certain point on, it pays off more to invest into damage instead. Weapon mastery + 2x DC + Goreriders are too much IMO. Therefore I would replace one of the eth DCs. You had the Zods for them, so you probably have another Zod for BotD. That will also add lots of leech. Another alternative would be a BotD GPA, a reach 5 weapon which hits the final WW breakpoint. Keep on your Goreriders then or perhaps even Goblin Toes.
I think you don't need any damage reduction versus councils. If there's something which might kill your barb, it's a combo of the explosion from fire/cold enchantment, conviction and lightning enchantment (edit: which you already mentioned
), something which DR won't help at.
Against conviction, you can put charms with fire and lightning res into the inventory. You don't need warcry skillers in PvM.
If your merc uses Reaper's, a couple of corpses will shatter and then you cannot hork them. You better don't make him good at killing then, but at surviving. A Tomb Reaver is awewome at that. I suggest 2x Amn and perhaps Shael if he can reach an IAS breakpoint with it. That weapon woll also max his resists which is essential in this case.
Or even better, you respec him into a frenzy barb
. I suggest BotD + Death in colossus blades as weapons. BAs look girlish on a barb while CBs have much more of a badass look and make cool
WHOOSH sound when being swung.