The Battle of the Omarion Nebula was a trap laid by the Founders. They infiltrated the Tal'Shiar, and were two steps ahead of the Obsidian Order and Tal'Shiar fleets.
At this point Federation, Klingon, Romulan and Cardassian shields were useless against the Dominion weapons. 150 attack ships were more than enough to destroy the fleet and cripple the Tal'Shiar and Obsidian Order.
The Founders were not on the World that was attacked. It's possible that the infiltrator changed Romulan and Cardassian records to show this world to be the Founders home, while the real home was light years away. Then devices were placed on the planet to give false life readings to her invading fleet.
And even if the right world was attacked, that it was a trap, false sensor readings would mean the Founders had just moved to a new world.
Now, what does all this have to do with the OP's question?