This blog post really hits the nail on the head as far as Deathwing's character being reduced to Gozilla-on-fire in Cataclysm.
I'm still plugging away at a fanfic that tries to make sense of it from Obsidia's POV, but I keep having to go further back in time to make it work. First I wrote about her thoughts the day he went kablooey at the Maelstrom, but moving on from that point didn't work until I had explained my version of the rest of the Cataclysm-era plots in BWD, etc., and then I ended up needing to flesh out the whole "Sabellian in Outland" thing, and pretty soon I was back in the second war with Deathwing using the orcs as porters for eggs. It's like writing a fic backward, basically. Heh.
Point being, Black Dragonflight lore is a total mess right now, and that's even without the further adventures of Wrathion in MoP.