Psylocks deal damage that can't be mitigated by anything except for Aegis and Forcefield. It completely ignores Block, Reverse Attack, Dodge, Guard, Armor, etc.
Basically they are a hard counter to the "big melee creatures on Guard" strategy (such as knights of westlock or iron golems). Compared to Brogan (who is also designed to defeat armor+defense stacking) the Psylocks are considerably more cumbersome (requiring a full action) but are Flying so they cannot be beat down by the golems. (Unless your opponent uses Knockdown)