Why are the pink L40 guns like the Brisk Polar Excess weaker than the Epics such as the Warfather's Sting?

Polar Excess - 48-54 Dmg, 0.8spd, 13 str, 3%hit, 1%crit, 60 health
sting (custom) - 51-100 dmg, 0.8spd, 7 dex, 6^ hit, 40 hlth, 40 mana

i love the look of my Excess but its so much weaker... so whats the deal here?