I'd go offense/defense tree, am happy with the Defense options you're seeing there.

Offense gets more interesting because you're locked into going down to Warmaster, but a lot of the other options just become trivial. That's likely why you see choices like Wrath.

The masteries at HellHades look good for CB. Wrath of the Slain has no big impact, but so do other possible tier 4 masteries. 

The only tier 4 masteries aviable following this generally good path HellHades gives would be Cycle of Violence (will never activate vs. CB), Harvest Despair (will never activate vs. CB) and Solidarity. The latter can increase the allies res to withstand the debuffs from affinity CB, probably better than Wrath of the Slain, but I wouldn't say that's a game changer. 

How about Solidarity in the defense tree instead of Wrath of the Slain in the offense tree?

After all Jareg sometimes puts 3 buffs on allies. Which would mean +15 resist to avoid those stuns, poisons and so on from the boss.

EDIT: I skimmed your answer a bit too fast Skadi. You actually agreed it's a bit better.

The stun is unresistable, actually

That's weird. I don't always get stunned. Does UDK have any mechanism that circumvents it then?

Update on progress:

I put Jareg as my lead. Replaced Kunoichi for him. I went from doing 14M-19M on NM to over 20M consistently(so far, 3 tries). This means I'm capable of 2 keys for Nightmare. I'm happy with that.

I also got improved my UNM considerably, but I'm really not ready for that regardless.

He will still get a little stronger. He is only 5/6 ascension because I need his 6th ascension point for a mission that's coming up soon. I already have a pretty good banner ready. EDIT: Oh, and Jareg has slightly worse gear than Kunoichi in general. 9k less power, some of which will be made up for with a banner.

UDK redirects the stun to himself 50% of the time

And the stun can't override block debuffs, if you have that up