You are creating a straw man here. I’m not saying that Cyrus fulfilled the prophecy in revelation, i’m saying the fact that he diverted the waters to attack Babylon means the writers of revelation had experience of the Euphrates being dried to prepare the way for a millitary crossing.This argument will not work because even if it were true, the "kings of the east" were not there to fulfill the prophecy.
In other words they were predicting based of past experience, not pulling the knowledge from God.