OK, you also seem to be completely not understanding the post telling you the issue.
"how much of a gargantuan undertaking it is to rework thousands of art assets that mesh together in a paperdoll system" IS the ENTIRE art side of it. A paperdoll system is what this and many other games use, with different parts of the body, clothing, expressions, exc drawn separately and then layered together in the game to make the full images. While there is some coding side to it, it's still a huge amount of art assets to make before the coding side can really get done (unless you use placeholder files).
I'll say it again, making the assets for the paperdoll system and making sure they mesh together properly IS THE ART SIDE OF THINGS.
The P-cup DLC also requires more redrawing than the H cup one did, since the larger breasts would interact with the rest of both Karryn's body and any others in a scene more than the smaller breasts did. They're also updating all the art assets, not just making the P-cup assets (setting aside the debates on the quality of those).
What has (likely) been happening, is that the art assets get drawn, then they get passed over to the programmer to put in piece by piece. So the artist draws the level 1 defeat scenes, they get added into the development build of the game while the artist goes to work on other scenes. The art assets don't need to all be done before the programming side starts.