Blizzard said layering affects queues themselves in this post:
While we are able to fit several times more players on a single realm in 2019 than was the case in 2006, we are not going to raise that cap any further, even though we have the technical capacity to do so. Raising realm caps would simply forestall the problem, letting more players in at launch but creating an unsustainable situation down the line, with severe queues when we turn off layering permanently before Phase 2 of our content unlock plan.