Just tried an increasing difficulty game, with final 5 on, starting at emperor... got fairly hosed as nearly all the AIs died to barbs, the AC shot up really quickly, and then blight happened insanely early, taking my size 15 cities (which had no unhealth before blight) down to size 1. And the AI now at deity seemed to weather the blight fairly unscathed; the combination of health bonuses (I suspect) and sprawling rather than concentrated growth.
I hate how blight hurts large cities worse than small ones; a city that is size 7 or so is fine and doesn't even lose pop, but a larger city shrinks all the way down to pop 1. I wish all cities just got the same increase in unhealth; this would still make larger cities suffer more because they have higher unhealth to start with because of more pop, but it wouldn't make large cities shrink to a smaller size than small cities.
Really hurts civs like Khazad (who I was playing) who need small numbers of large cities because of the Dwarven Vault.
Blight at AC 30 is pretty damn annoying too.