I'm curious if the damage output for this weapon would exceed that of the ballistic fist when you factor in the 3X critical chance.
It depends on how much crit you have, if you took Heavy Handed or not, if you have Better Criticals.
I think the max possible DPS of the Mantis (100% crit and Better criticals) is higher than from the Ballistic Fist though (max crit 38%). But I'm not sure of the exact formula of how Better Criticals applies, or if the Crit bonus damage scales in other ways, etc etc. Also vs enemies with more than 15 DT (so Piercing Strike no longer negates it all) the slower but harder hitting Ballistic fist gets a leg up.
Obviously if the Mantis is fixed to actually ignore DT that is a huge bonus, plus you get to save a valuable perk (I've found there are a lot more "must have" perks when playing as a melee character).