About nsp sizes: i've used different methods to obtain .nsp files (i.e. by downloading or convertion), and what i've noticed is the resulting .nsp
from CDNSP(GUI) all appear(ed) to be much bigger (about
50% increase in size) than the ones i downloaded from XCI/NSP download websites.
I wasn't able to compress the .nsp in question, which makes me believe one of the .nsp's either wasn't of the same game version/update
or used a different way of packing/compressing the .nsp contents.
About the tool: I can see a good use for it. Awesome sause!