Weaken has +200% Cap. keep the Weaken on the Pet and take off any Epic Weaken (Orange) on the other items. +90% Weaken is good for a minimum, but having +100% or higher is better, since all attacks will be Weakened, not just 90% chance for 90% Weaken.
here is a Post on why Weaken is so good.
find a Flintlock with +200% WD.
for future reference, Crushing Flames Set requires a Fire Weapon or Prismatic Talent (Wizard), Ascendant Set, or Elements Set, and also you need Crushing Blow. without both Fire & CB, it won’t work at all.
an addition to adding Frozen Set, take off one Pathfinder & add Permafrost Set.
when you get a Flintlock with +200% WD, try for a Crystal +225% Crit DMG. this way you still have over 100% Weaken, and you only need 2 more spaces for +75% Crit DMG for Cap, and you can take off any others for other affixes.