The problem here is the Flood of Light wouldn't do anything for Elidibus at the moment because without Black Rose there is no pending calamity that we are aware of to allow a Rejoining to take place. That would be counterproductive for Elidibus to do to say the least. My guess goes back to his speech about wanting to 'keep us mired in the first', it seems to be an action more to disrupt our progress specifically. But how he intends to do so? That's still a hard thing to determine, as he basically creating a bunch of people with hero complexes.
My theory he intends to mislead these heroes against us somehow, maybe by creating an illusion of some kind of threat, though I must say trying to pin anything on the "Warrior of Darkness" normally would be difficult. Then again, get enough people who think they're doing the right thing and I wouldn't be surprised on what they could do.