Disruptors are Vicious, not piercing.
So far as I can tell there are no mods for disruptors.
There is no way to add piercing to a disruptor. I suppose you could jury rig it but at the expense of having easy critical hits.
Sure you can activate a critical easily but so what ?
You are absolutely right. Weapons are scary. They kill people. That's what they are designed to do.
As far as I remember only range increasing and Additional Shot Attachments are prohibited for Disruptors, not Damage Increasing ones.
also yes, weapons are scary, even without your interpretation of pierce, event he Holdoutblaster is scary for almost everyone, ecept High-Soak chars, and for those, still everything starting at Normal Blaster Pistols everything is scary, so I don't see a reason for your interpretation, wich has it's logic, but I don't really think it was intended that way.
I also found a passage concering Soak, where it said "Some weapon Wualities MODIFY the soak of the target" in my Copy of EOTE Beta.
If you and your group think they have more fun that way, I wouldn't dare to stop you from playing that way, but I wouldn't like it, because I really hate random deaths.
A deadly system is fine, as long as I have some control over "not trying to die" and don't get the feeling, that it isn't in my hand in any way shape or form, if I die, because the RNG said so.