What's interesting is that Rowling has expressed regret that Order of the Phoenix, the longest book in the Potter series by over 100 pages, ended up being as long as it was and that she wished she had cut some subplots out. Half-Blood Prince and Deathly Hallows were much shorter as a result. So kind of weird that she's slid back into this habit when it has bitten her in the butt before.
However, I'm not surprised that an editor wasn't able to get her to trim things down, if they even tried. It's become abundantly clear in recent months that Rowling has forgotten what it's like to be told no.