None,he is an author that mostly keeps to CG sets.
Two of his works have been adapted to animation though(well one and a half since Gaki is taking its sweet ass time to actually conclude).
Which one? Since most of the Avatar cast were teenagers, most of the females, while not busty, were at least curvy. Only 'true loli' character here is Toph or maybe Slave Route Jinora. This game seems to exaggerate at best. I can't think of anyone TERRIBLY off-model, which is why I like it.
You asking who was changed or who should be flatter?
Far as the former goes that would have been Katara with the size-potion.
For the latter...really most of the first three books main cast is rather exaggerated.
Though if you are looking for flat-justice...yeah as mentioned Mity certainly tried to avoid that for the most part(you also forgot that there is a Bee flying around in book 3).
That aside,would suggest thinking twice about using a word like "true loli" these days.
You never know who reads the topic and might misinterpret.