Spoilers for the ending of the main quest.
1) As it stands, in the end Melissa trades Hade's life for the life of your starter slave (assuming you haven't let them go or killed them in battle with your superior tactics) most favored slave (as per Rendrassa's clarification). You have a choice to either spare Hade and let them both go or kill Hade and enslave her, letting your companion die. If you do not have any mansion residents at the time of battling Hade, Melissa doesn't show up (presumably because she has no one to take for ransom) and you just defeat Hade and never see him again. So, why not let us enslave Hade when Melissa doesn't come, or let us allow Melissa to kill our companion and then shackle her and beat the bejeezus out of her to get them both? Or at least kill her instead of killing Hade?
As an aside, I also feel like if Melissa tries to capture someone whose magic affinity is higher than hers, the captive should be able to at least try to escape on their own, but that might just be me.
2) It would be nice to have an option to enslave Garthor instead of just leaving him beaten on the ground or outright killing him. Doing either of those things feels like a waste.