Heavy stun doesnt feel good vs hard bosses

To many hard (t4 difficulty bosses) are more or less immune to stun. I built a titan fully dedicated to stun and stunning a boss feels nearly impossible on around a 200divine character.

Suggestions

(insert name) keystone or piece of gear - elemental damage contributes to stun build up - physical damage does not

Explosive impact keystone - you have 20% less stun threshold, enemies have -30% stun threshold

keystone - all or nothing - ailment magnitude modifiers apply to stun build up at 50% effect

also generally speaking, the defense layer options in the bottom left of the tree are terrible. life is in a terrible spot, armour is in a terrible spot, hybrid evasion/armour is in a terrible spot. There are no interesting keystones like acrobatics/ci for life/armor builds either.