Yes, I think your overall proportions are mostly fine, it's a matter of little details and how things are shaped. Notice the length of the arm, the thickness of the thighs, width of the hips and size of the feet. The arrangement of the face should also be considered. And to some extent, I think it's the men that look more babyish, and when I notice it in a male character, I realize that the females are cut from the same block and it all feels weird.
And I mean, it's art. There's not a right way to do things and you're not bad at drawing, it's just that they're not sexy. Art reference models are often very plain looking, and art references poses are either very stiff or very strange. And realism is not necessarily desirable, porn is generally supposed to be fantasy, an escape from reality. If you're making porn, it's better to use pornstars, pro models, actresses, etc. And when making cartoons, I would suggest analyzing other cartoons as well. I know that a lot of serious art teachers frown on that, but it can be very helpful as long as you have enough knowledge of reality. And I get not wanting to make "bimbos". There are many body shapes and they can all be sexy.
Another thing to consider is the idea of drawing emotions instead of drawing things. Not necessarily human emotion, but a sense of drama or action or history in the subject, something you can emotionally respond to. Like, consider the difference between these two images:
Spoiler (click to show/hide):
Relying on orthographic art references can give people the same problem with drawing humans, you end up with a human diagram instead of human spirit. Playshapes was great at capturing this, and that is why people like it despite the obvious anatomical errors. In the comparison you posted, you can see the difference in the way Playshape's model is angled and curved and the pose of the leftmost model compared to the others. In more advanced poses, you are looking at things the angle of the shoulders and hips, the gaze, angle of facial lines, arms, legs, hands, curve of spine, line of action, etc. It's tempting to want to make a neutral pose to start out with so you can add emotionality on top of it, but a human is never really completely neutral. You never stand up completely straight and gaze dead ahead naturally. Even if a human is asleep or dead, they are not completely neutral. So it's not necessarily "correct" to make the human's baseline state a neutral one. At rest, they probably still look slightly smiley or annoyed or curious or aroused, etc, depending on their character. You have done some good work here, but there could be more.
For improving the animations, let me suggest this video series:
https://www.youtube.com/watch?v=haa7n3U ... i92U_l6ZJd This is absolutely something I wish I had been studying decades ago.
As for hair, in 3D animation, there are tools like latice deformers or spline IK that you can use to handle something like hair that doesn't bend rigidly. As a vector program, maybe Flash has some of those you could use to bend long hair without chopping it up? Unfortunately, I don't know my way around that side of Flash very well, I never much cared for 2D vector graphics.