None of the X Chance flags affect enemies until they're doing HP or Lust damage. Special Attacks (i.e. Paralyzing Shock, Overcharge) can inflict status effects through Shields/Armor.
I'd still recommend Stun or maybe Vampiric. A surprising number of enemies have no/negligible Shields. For those that have significant Shields, they're usually vulnerable to Electric damage and you should have a lot of that with Charge Weapon.
Stun: Provides 2 turns for Rapid Recharge to negate damage taken, prevents special abilities (including healing) and guarantees follow-up attacks will hit. That said, Stun is hard to get (only from Dull Behemoth Crystals), and there are already a lot of good Stun Melee weapons.
Vampiric: Tech Specialist has no native healing. There are a handful of attacks that ignore Shields. Weapon crafting is currently the only way to get it on a melee weapon.
Drain: Only works on Shields (Armor/Chitin/Wings/etc. don't count). Only works while the target still has Shields left.
Don't discount high Crit (caps at 50%, so don't over-invest).
