I agree with you on most points.
However, the facial looks the characters have do vary beyond your description. Yes, there are some bland looks, but there are many very spot-on looks. Ashley has amazing eyes that convey her innocent nature. The neighbor, Sophia, has that angelic look and personality that does not need extreme facial expression, but you get her meaning nonetheless. I think it's a case of coming across an occasional bland or a not quite spot-on expression and later thinking all the expressions are that way.
At this level, you have to give the
Merizmare credit for the amazing work. Go back, and you'll see many very good expressions.
IMO, dialogue having a very natural flow is very important to immersion. In so many cases here on F95, it's the math and reading metaphor. We mostly all read better than we do math. In AVNs, the art is reading, and dialogue is math. We are visual animals predomitly.