ok, wep skill increases MINIMUM damage and wepskill(chance to hit and not get evaded/parried/blocked)plus styles, CD is styles and +% to offswing, piercing stat=str 50% and dex 50%, blades and crush= all str.
and YES O GOD spec 25 pierce, diamondback is a 5 second stun first style in an evade chain. it is the best style in the entire line, because if u r ranger/ns(and mebbe BM) u should use pierce because u have good evades, especially ns.
faster swing=more poison(ns) more dmg from ur dmg add buff(ranger) and more dmg anyways(all)
Hope this cleared it up.