Resiliance should increase resistance to spells and armor pen by the same amount as it currently decreases crit %.
So you could have:
12.5% less player damage
12.5% less crits
25% less damage from crits
25% resistance to spells
25% resistance to armor penetration effects
Then make all pvp gear 5 stat items with a full set counteracting the 25% resistance to spells and 25% resistance to armor pen (aka casters get 25% spell penetration and melee get 25% arp)
Finally add a debuff to the shadow sight icons that gives a 100% mortal strike for 10s effect to prevent matches from going too long.