while the style and proportions you are now achieving are indisputably better than your first attempt they are inherently flat, and if you are trying to portray them "flat shaded" then great, but here's a quick example of how you can use more tones to bring more volume into it
just scribbled in quickly with a large pixel brush, colour grabbed from the lips, and is far from pillow shading, the shading on your first was inconsistent to a light source and the highlight 2 tone with banded shading, so don't avoid highlights altogether just those types of highlights, always try keeping the light source consistent
also figured it might be helpful so i quickly whipped up this
to show you what you can get away with and to illustrate different lighting angles and intensity of highlights (and thus the light being shone)
note though that it's haphazard and rushed so don't follow it too rigorously as I'm sure it wasn't as well thought out as it should be relating to the volumes, but hopefully it's helpful