You have described what games of the past have done.
I cannot find any fundamental limit in your argument though. Those are all problems that could be solved.
Also I dont see that there are many variables for the body:
- height
- width
- fat amount
- muscle amount
- length of appendexes (arms and legs) relative to body size
- size of hands and feet relative to body size
Thats pretty much all I could think of.
But even if one could only vary height and width that would already make sure that there is more visual variance than there is now in BG3.