The scary thing about the super death qi exploding ball wasn't the explosion. Rather, it was the death qi that followed the explosion.
About a thousand square meters worth of flying fish beasts were gone in a blink of an eye. That wasn't the end of it, though. Rotting essence formed in the air the sea. The death qi of a perfect skeleton was just activated.
The flying fish beast pack didn't seem to be afraid. Instead, they continued to rush in the same direction as before. It probably had something to do with the geography. While death qi could stay in the same place for a while if it was on land, if it was in the ocean, the water would simply wash it away no matter how many corpses were generated. The ocean could wash everything away.