Gesture of Pain ignores the damage bonus from psiblades.
I can't recommend a complete build. It's impractical to not have points in shadows by level 50. So Advanced Shadowmancy becomes less of investment. Here are some options for clearing hard dungeons.
1. This playstyle is much worse with auto-expore.
Hateful torque of mindblast 4 hate or better(buy it), mindstar of sand(buy it) combined with movement infusion, advanced shadowmancy(damage scales with shadow warriors, mindpower, mind crit, crit power), wand of clairvoyance. Try to get tracking or arcane eye form escorts.
You can restore hate. Rest, shoot the hateful torque, repeat a few times.
Turn off call shadows to avoid detection. Dig instant tunnels with the mindstar and movement infusion, use wand of clairvoyance, send shadows through the walls from relative safety. Merge for hate (you can target the same shadow twice). Shadow's Path allows to position shadows to bait from longer range or to make fewer monsters alert. Shadow senses enables shadow's path and cursed bolt to work as if you could normally see all shadows.
2. How to disable damage from a single opponent.
Ruined Earth(-50% damage debuff to all in area radius 8 for 8 turns, the debuff lasts 3 turns, CD=30 turns), Merge(-48%, 6 turns max, CD=6), Feed power(-16%, +16% to you), melee numbing darkness(-15%) and slow. Torques with psionic shields are useful against their damage bonus. All of the above damage debuffs are additive.
3. Elemental Fury with Mental Tyrany and Madness. They split your damage into 8 pieces. That's 4 possibilities for madness, 8 ones for ogre fury. I hope ogre fury works against your own deflection.