Hello,
We don’t want to merge the paragraph font-size and line-height with the body styles because paragraph font-size is larger than body font-size by default. So, we created a separate option for paragraph font-size. We left the default line-height – 1.6 because it’s optimal line-height for the text no matter what font-size user will use. In your case paragraph line-height is 28.8px, at the same time you set the body line-height 30px, it’s not a very big difference.
Regards