Punishment only will only work for selling low-tier low sensitivity slaves. I tried to make it so you need to balance punishment and rewards.Congratulations for your mod! I placed it in the OP so people can try for themselves if they want to
I haven't tried, but from why I read and understood, you disliked how "not dark" the gameplay expected you to behave towards your slave. You're more "punishments only" than "punishment and reward".
Feel free to correct me and the short description of your mod I gave in the OP.
Also I wanted to say that we made sure fear based obedience would work for any action you ask your slave to do, including the most vile. So the vanilla gameplay isn't so far off what you propose with your mod, at least in principle
I wanted to change the gameplay to put emphasis and increase the difficulty on the part I found fun, I.E. getting your slave to become obedient, and remove the part I found to be just tedious.
The game is perhaps darker but if you want to only use some verbal punishments to get fear to 3 or 4 you can still do it like that. Then build up other aura stats and you will be fine. That wasn't really the intention. At the start, a low-skill trainer is probably better at using brute force methods to sell low-quality slaves but it won't work for B+ and above slaves.
The big change is the core gameplay mechanics. The goal in training is to get to full obedience without draining the aura stats of your slave, making her less valuable. I tried to balance the game around this mechanic. It's not a perfect ATM as I didn't spend too much time on it yet. The most important stat is now the sensitivity and how it interacts with despair.