the issue was that gods were very hard to get rid of in Theros and Born of the Gods. The required something like Detention Sphere to really take care of them. Sure, you could also run Revoke Existence, but that was a very narrow answer. Deicide is JUST as narrow a card, except it takes care of other gods (of the same sort) too. It's really quite flavorful. Gods were supreme for the entirety of their history on Theros (Theros, the set). It was only when Xenagos decided to usurp the natural order that things changed (Born of the Gods--Revoke Existence, Unravel the Aether, Gild). Elspeth was called to action, forced to wield the empowered Godsend, and take care of business. Now the populace is aware of just how wrong they were about their gods (Banishing Light, Deicide, Silence the Believers).
Honestly, you deck shouldn't revolve around any one card. That makes it way too easy to disrupt. I'm not sure the Gods were a cornerstone/4-of in any deck except Monoblue with Thassa and Monoblue-splashing-white with Thassa and Ephara. That's really the only place Deicide will REALLY punish the deck.