Is this a bug in Seaborn?
From the seaborn documentation:


  scale : {“area”, “count”, “width”}, optional
  
  The method used to scale the width of each violin. If area, each violin will have the same area. If count, the width of the violins will be scaled by the number of observations in that bin. If width, each violin will have the same width.


So the violins are scaled such that the width is proportional to the number of observations. You were expecting the area to be scaled with count, not the width, and that seems natural to me but that option does not seem to exist in seaborn. Here is an issue regarding this, with a handmade solution:

https://github.com/mwaskom/seaborn/issues/962