I like ars diabolos on the build, gives more overall utility to the build, you can socket it + make up for a few loss dmg or - res in other parts of your build/gear

in my setup it's the only place to put ancient socket

So I tested it offline bit more, ars vs phoenix, you destroy anything p8, so the only area which makes sense to measure is dclone or p8 herald t5 which takes longer. Ars pumps more, i spawned p8 dclone, which should be 95% fire res, conviction12 brings it to 10 and anything from gear brings it to 0% any anything below 0% res is +%fire damage, where ars + fire % enemy damage and - fire % res gives more overall than -28% enemy res.

The -% enemy res is hitting diminishing returns in short with phoenix, warock has enough from other sources. And the redemption aura is not that great, ars has maek + hex siphon. I use barb bo so it's no-pot, which would be otherwise motivation for redemption.