Yep yep, a valid point. I made a post about this when layering was announced. It is indeed a Risk. I also made a post that the bottleneck of begining zones is a joke, and it ruins gameplay. Even 3 layers wont be enough at server launch to stop the begining zone bottlenecks where you’re spending 1hour on the boar quest. That is not good either.
It seems they are using layering to avoid bottlenecks, but IAN also stated they are using it increase server concurrency. That by itself isn’t the best idea because of what you stated. If classic indeed has high retention rates, then you have servers that are literally 2-3x more the population cap than the world can actually hold, which means layers will never actually be removed because then you would have 3x the players in a world that can only support 1x. I gaurantee you this will happen on at least some servers.
So hopefully they can figure something out. They absolutely need some form or sharding or bottleneck prevention for the starting zones.