Question says it all. Here's how it came about.
Me and a friend were discussing his getting into 8th edition. And it came to Demons breaking 7th ed. I said it didn't. Sure, some rules greatly improved the effectiveness of demons, but I don't think it broke the game. IMO, if any army was to have broken 7th ed, it would be, to me, Vamp counts, with spamming some spell I forget.
I don't mean this as a slight on 8th ed. I would love to get into it, but time and other things keep me from it.