I liked the early WCA arc myself. The Byrne arc kind of came out of nowhere. Her 2 souls issues had been resolved and then, for no reason I can remember, she suddenly started taking on more and more catlike characteristics.
Agatha Harkness helped her resolve everything. But, unless I'm forgetting a plot point, there was never any explanation about why she was having the problems again after her 2 souls (human and cat) had been merged.
I think I remember that Byrne cut parts out for Acts of vengence, but it was resolved in solo avengers.