I'd be fine with slashing/piercing if all the classes that need them had them to be honest. MCH/BRD both should have Piercing on Straight/Hot Shot and DRK should get Slashing on Plunge. PLD certainly could get it as well (likely on Goring Blade similar to NIN) but given people aren't running dual PLD comps it would be fine as long as two of the three tank classes had it. It benefits PLD the least out of all three regardless.