Occult Slayer has border line immunity to spells at the level 20 core. If anyone bothers putting more than a couple points into that tree, it's to get that ability.
Frenzied Berserker gets +10 melee power at 18 and +10 melee power, big damage on vorpals, Storm's Eye, and +4 con at 20.
There isn't a splash that gets near equaling the kind of power those capstones give for barbarians.