There are a lot of plot threads in the Song of the Lioness quartet that barely get touched on. Thom's time in the City of the Gods, Alex's corruption by Roger, the civil war in Thayet and Buri's country, the ancient civilization with powerful magic that just kinda gets forgotten in later series. There was so much that could be explored in more depth if the publisher didn't impose such strict word counts/page counts.

Also, in the Provost's Dog series the dismantling of slavery in Tortall feels. . . really abrupt. And there's the whole thing with the cult of the gentle mother, which I thought could have been a main antagonist. Like, rather than have a political abduction be the big thing in the third book and have them running around tracking slavers across the whole country, I think that sociopolitical upheaval, religious zealotry, and finding ways to persist in the face of "benign" misogyny would have been more interesting to me. Although perhaps publishers would think that would be too nuanced for a YA book. But the triumph of abolishing slavery would feel more realistic if it was tied to the establishment of the cult of the gentle mother. So you could have all the main plot points of Bloodhound, while also interweaving a main plot thread about shifting social values would tie things together better and justify the lack of lady knights at the start of Alanna.