Hard time with lair bosses

Trying out Spiritborn this season after using Sorcerer and Druid. The other builds are able to clear T12 stuff easily and destroy any lair boss in a few seconds, but Spiritborn is really struggling on bosses, even the easier ones in T12.

My build is basically a cut / paste of Ignition's build on Maxroll except for a few changes. My charm only has 5 slots (20% Damage, 20% Damage over Time) so I can't equip a unique charm. Been getting really unlucky with charm drops. Also using Shattered Vow with Supremacy on the amulet. I have a decent legendary polearm with Supremacy and an amulet with Writhing but the Shattered Vow variant clears pits much better and also does better on bosses.

All glyphs are over 100, affixes are pretty much in line with Maxroll too. Helltide and Pit up to level 115 are no problem but I can't beat some bosses.

Any ideas would be helpful. Thanks inadvance.