I disagree that Sirens should be made immune to the Neural Disruption ability. Even when their psychic powers are nullified, Sirens are still tough, fast and dangerous enemies that can still attack effectively using their Slasher/Injector Arms or Acid Torsos. The Neural Disruption ability of the Disruptor Head seems like it was specifically meant to provide players with a hard counter option against enemy psychic powers. It’s more reasonable than having to outfit whole teams with Clarity Heads/Ignore Pain to protect against Mind Control, or having to kill/head cripple every psychic enemy before they get close to your team.
But I do think that there is a case to be made that Neural Disruption should be rebalanced due to it nullifying enemy psychic powers a bit too effectively and easily. Maybe it could be changed so that every time an enemy is Neural Disrupted, that enemy only has their Will Points reduced or has their Will Point cost to use abilities increased, for example.
If Neural Disruption in its current form is overpowered, what suggestions might you have for rebalancing it?