In terms of immediate impact, Eris' actions definitely had more.
The darkness she summoned instantly encompassed a wide area around her and created an impenetrable domain.
August, on the other hand, didn't summon a massive amount of his element immediately. This space wasn't really able to contain an ocean. August had taken control of the underground rivers and reservoirs and was keeping their power hidden until he needed it.
Though, they wouldn't remain hidden for long.
The battle had changed from close combat to ranged. The two geniuses didn't approach each other and instead summoned their power with the time they gained from their separation.
Eris moved first.
'Dance of Ten Thousand Demons.'
Her arm raised parallel to the ground and a huge amount of mana burst forth. The darkness around her morphed, and an ability that August had seen already returned to the light.
