I think the Tholians used slaves in their study of the Defiant mostly because it would be toxic for them to enter the ship themselves. If they were to increase the temperature and pressure to match what they are comfortable with it would potentially destroy important equipment in the Earth ship. They could not use the ship itself- it was far too alien to them, but they could harvest the technology for study.
In the ST-E episode 'Future Tense' we see the Tholians making a reappearance. the first since TOS. What I really like about this episode is that their motivations and behavior are still baffling but their technology is very formidable, even without their iconic web.
In the ST-E episode 'Future Tense' we see the Tholians making a reappearance. the first since TOS. What I really like about this episode is that their motivations and behavior are still baffling but their technology is very formidable, even without their iconic web.