It could still fall under the heading of routing, just not the kind that anything can be done about at least on our end. Your ISP or VPN can only reroute you to a certain point, once it gets to that point in the route, thats the only way it can go to get there, i would guess this would be the backbone for the datacenter though it could be before that. If theres not enough bandwidth to support the amount of connections to the datacenter on that primary route, then it's going to get congested easily. That being said, it could also still be the networking hardware not being capable enough to hand the amount of incoming connections, hence why most mmo's usually split up NA and EU to their own datacenters. Heck, iirc blizzard uses MULTIPLE NA datacenters for wow, i think they've got both west coast and east coast ones. Though maybe thats a different MMO i'm thinking of.