Honestly, I don't think Cassandra was in the book enough to be "mangled" and Barbara seemed in character enough to me. Certainly in at or about the same state of mind she was at the end of BoP. Now, you can certainly dislike that turn her character has taken but it is a lose/lose situation for a writer. If he just creates the version he wants, he gets yelled at for ignoring continuity and he's clearly demonized for writing the character he's been given.
The truth is, I am a bigger fan of Batman's supporting cast than I am of Batman. Or more specifically, Bruce Wayne. Dick and Tim and Selina and Cassandra and Stephanie and the Huntress and a bunch of others really draw me into these series of books. But I think I would literally go crazy if I got completely out of shape of every character moment that wasn't "optimal" for me. The closest I got was when Spoiler was dead in the first place and they fixed that eventually.
Give it time, I think. And try and let your preconceived notions of what your perfect character should be go. At the end of the day, this is still worlds better than Cass being a murderninja who just hates everyone. Two pages of (relatively) cogent and actually reasonably happy Cassandra are infinitely better than 12 months of psychobitch.