Points for fashion, that is one cool looking character. But I got to agree with Smish.smash.smosh here on the lack of RR.
Devouring Swarm should be maxed out, and missing Rattosh is… painful, it not only is your big source of of vit RR, it also reduces enemy life leech resistance which makes a bit differences against bosses.
So you’re missing about 50% RR from just skillpoints and devotions, and could get another 20 from rings if you wanted.
For a spam build, I’d also consider the Wildblood Crusher instead of Nightbringer. Nightbringer is an amazing weapon, but the lack of attack speed hurts this build a lot, and Wildblood also has a lot more flat damage and extra life leech RR on Swarm. (And some extra damage.)
All you lose in return is some Conjurer skillpoints, which won’t hurt the build much, and some conversion. But you don’t get much flat acid damage to convert anyway, just a bit from Blood of Dreeg.
The bigger loss is the proc, the summons look cool and reduce enemy damage, so you might want to find a different source for that debuff.
Oh, and one more thing I myself only learned recently: The second node of Primal Strike, Torrent, is an “secondary” effect that does not stack with the primary ability. So it’s less useful than maxing out the last node, where the flat lightning damage is added directly to your attacks and multiplied by the %WD modifier.
Gear and devotions. Some skills have masteries that help. (Shaman does, but only on Savagery and Stormcaller’s Pact, which you don’t need…) Components too, like Mark of the Traveller on boots and Topaz on rings.
Slow res is essential for spam skill builds like this one. Freeze res is less important, but can kill you if you lack it and meet Moosilauke, and the new expansion added a lot of freezing enemies.
One great way of fixing it is crafting some Intrepid Warboots, it comes with hefty native freeze and slow resistance, and can roll affixes that add more.
