Then, if we consider that this power is selective... Why did Orpheus choose to use it on the Emperor in the first place? Literally the Emperor only regained his individuality after being affected by the power.
I think this makes more sense if Orpheus didn't use it on the Emperor in the first place.
According to the elder brain, "When the Chosen sent my thralls to retrieve the Prism - who do you think let the 'Emperor' slip its leash, knowing it would be the one to bring you to me?"
I take it that the elder brain deliberately ended its control over the Emperor, but did so in a way that the Emperor mistook it as being caused by proximity to the prism.
