Our dog park group has extremes, several of the girls are very petite, weighing 15-16 lbs and looking great. There are a few very tall and slim boys, and a couple who are tall and, hmmm, not slim! Basically, we have the full spectrum of body types, some people are surprised they are the same breed with all the colors and sizes.
Sounds like you just have 2 ends of the spectrum, both look great to me.