I am going to heavily borrow from Cold Shadow for a moment here as I had the same thought when reading through the thread but saw he posted it first.

If you changed this "freeze" damage to some form of "elemental" damage type (e.g naturally occurring - like fire) and then removed PSI resist and replace it with elemental resistance then this would work.

Freezer guns/shockers would then be viable to hurt low psi using people and those with high psi attributes could afford to spec the points. Obviously these weapons would be balanced in line with TL etc with the advent of Sparta.

Tanks using the shocker would now have a weapon to beat other tanks with (they have no psi and therefore no resistance to it).

PE would have the option to spec some psi resist at a cost of his other defences (psi based) and the Spy would theoretically have high(ish) resist due to having 20 levels to spend if he didnt want to use psi buffs.

Everyone would have access to the weapons (cannons rifles and pistols) and you could add elemental damage to some APU spells and possibly EVEN give the ppu a very low level Elemental damage spell vs mobs although this last part is a reach.

This would throw a new angle into armour/resists conundrum especially with the forthcoming balancing changes to armour that got hinted about a while back.