I haven't played Warrior's Guild because I want to finish it in one go when it's ready instead of going back every week to play a couple new scenes so I can't do an overall comparison between Yvonne and Ada's scenes even if I wanted to. That's why I stuck to describing the pictures. And while the black blob might not be ideal, I still prefer it over Ethan being the focus. I want the MC's expressions and decay to be the supporting role to showcase each mistress. Looking at the pictures I feel that Ada is better showcased rather than Yvonne who just seems like an afterthought to you satisfying your addiction. If that isn't the case, it's because the writing and/or gameplay for Yvonne is better and makes that scene better overall, not because of the art.
Seeing those 2 pictures makes me remember the distinction between someone who serves just to satisfy his lust and someone who serves to satisfy his mistress. And while in the second picture it's unclear what your motives are, at the very least with a glance you understand it's something that Ada enjoys. In the first picture it's clear that your motive is just satisfying your lust.
Btw, I can't take the decay concept seriously in ToT. When you start the game, Ethan is like "I want to save my friends at all costs!". You get your ass kicked by Scarlett and after a while he becomes "I'll abandon my quest so I can serve you better mistress!". Then she allows you to go climb the tower for reasons I've forgotten, and once you get to the next floor you're at "I want to save my friends at all costs!" mode again. Rinse and repeat for each new floor. And I understand it's hard to do anything else, since the devs don't know if you submitted to the last boss or not, but nonetheless it loses its impact after seeing it happen again and again. Even if he falls deeper and deeper, once he goes to the next boss with all traces of past corruption gone and possessing a rediscovered supply of misplaced confidence, then any semblance of immersion will be broken.
With that in mind, I see them spending time to flesh out Ethan's decay instead of developing more CGs for the women as more of a negative thing. I do like it that it's not just a blob in ToT when Ethan is getting bullied by the mistresses. For instance looking at the CG of Lily shoving her stockinged foot in Ethan's mouth, I think that image would be much less hot if you replaced Ethan would just a blob. But if I had to choose between extremes like fleshing out Ethan so much that more than half the pictures are of just him, or having the game be first person perspective like GearlessJoe suggested, I'd pick the second option in a heartbeat.