That skill deals 500 piercing damage and yet kills a 750 hp+375 shield Fire Prism in one hit. (Notice the wraithguards who only lost half their shield from that same shot). My guess is that the shot deals damage to both the front and rear armour of the FP. Could also be that it has a secret damage bonus vs. skimmers, hopefully unintended.
(you can find the replay of 2 FP killed with a single shot by a KP on the Discord, or ask me there for a re-upload: https://discord.gg/GWpr6x)