@Nirwanna: Those two things are not directly connected to each other. We are merely better informed how the various realms look in comparison to each other.
I am sure they do not count towards that big a drop. That some players have predicted such heavy losses is an entirely other matter.
Actually, because turning layering off means that the CCU cap gets axed, it is an advantage to pick a layered realm, because having layering on means that the activity is still high and there is less probability for needing to stay in queue. If just a single realm has layering permanently turned off very early, it means it is bleeding players like no tomorrow.
There is only one problematic situation that can arise in the upper end, the population activity remains so high that even after layering goes and CCU cap drops, the queues are too long as phase 1 ends.