I posit that at least one of the SKs has instructed his/her underlings to not bother with torture beyond beatings, isolation, and starvation.
The next step in information gathering by these underlings would be done through either psionic mind-reading or necromancy.
For the latter, there might be a special chamber in the palace or templarate, enchanted by the SK or a powerful templar or defiler, that prevents the spirit of anyone killed within from escaping to the Gray. A necromancer can then extract information from that spirit. There would be a simple method to allow the spirit(s) to depart to the Gray when the information gathering phase is done so as not to overcrowd the chamber.
I tend to agree with you that torture is of limited application in the context of mind reading abilities. That said, we must not discard the torture trope because we lose so much good material.
We must consider what the purpose of torture is in this context. I would suggest that torture provides a penalty to the saving throws of the victim, so that characters that might otherwise resist mind reading cannot.
A chamber likes this would probably be more psionic than necromantic on Athas. I can see psionic crystals holding one or more souls/psyches in containment ala a psionic Trap the Soul-type power. Like the Crystal in the The Darkness Before the Dawn
It could be that there are psionic libraries where both willing and unwilling individuals were contained in psychic crystal to commune with, hell I just gave myself an idea for a short article!