If you've got the items, then you should be alright. Your build is pretty similar to the Convictor build I like playing. It's not a powerhouse by any means, but it's novel and pretty fun. Your builds would be much more effective against bosses, but as I mentioned earlier, you wouldn't be the best choice to tank for too long without a lot of pots.
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Convictor uses spell-procs and elemental damage added to attack (e.g. Meteor from Dragonhead, Blizzard from "Rfit", elementalist set) to do most of his damage. His char screen listed damage is about 5k, but he clears trash fine solo (just doesn't clear as fast as many other builds). In his case, a lot of his damage is not listed on the char screen. Of the damage that is applied to monsters, it's multi-element and the monster's resistances are greatly lowered.
I'm guessing what disheartened you was the lack of aura-stacking for -res. It's really not a big deal because of the way breaking immunities works. If the monsters are immune, then all of the auras and curses applied to break the immunity work at 1/5 effect, so the lack of aura-stacking from the Holy auras means you only lost out on 4%. If the monster was not immune, then you lose out on 20%, but you've already lowered it by 80-85% with Conviction, so the change in damage done by your party is negligable.
Here's a quick example, assuming your partner has 40% elemental pierce and did 1k dmg with their attack:
1) Immune monster brought down to 99% res via Conviction, then down to 59% via passive pierce:
- with additional -4% from holy aura stacking, your partner does 450 dmg
- without stacking, your partner does 410 dmg
2) Non immune monster with 0% res, brought down to -85% via Conviction, then down to -125% (I was once told that -100% this is the cap, but can't find a good reference, so I'm ignoring any cap to prove the example) via the passive pierce.
- With additional -20% from holy aura stacking, your partner does 2450 dmg
- Without stacking, your partner does 2250 dmg.
As I said earlier, since you've already got the gear lined up, you should be fine. Just don't expect to tank bosses without pots. My Convictor didn't even bother with LifeTap, since I just flashed Redemption when needed.