1) Ghosts now have more HP (twice as much!), so they're harder to kill with magic (the only effective means against these beasts).
2) Specters have more HP, so now each unit of mana yields more meat on the battlefield.
3) The casters themselves have more mana, which has become an incredible gift for specters!!! Now specters not only convert 1 unit of mana into 24 HP, but they also do it in increased quantities. For example, you can drain 17 mana from a spell-casting Mistress, which gives 17 specters, equating to about 408 HP. That's practically the same as Raise Dead, just without the cap.
So, if anyone has benefited from the patch, it's the specters — they're much better off now. And if they had kept their damage, the balance would have been completely ruined — specters would have become even better than skeleton archers...