Seems like their whole f******* login infrastructure wasn't designed for an MMORPG.

It has to handle the following on a more basic level:
-connection from all around the world
-allocate them the respective realmlist
-queue system

Looking at the number of people that alone should be enough to crash the server, but fear not, they increased the load by 50-80%, because:
-they disabled the queue, i.e. people hammer the server
-afk players do not get kicked out of the game, i.e. the open places are rare

But don't worry, that's not all. From the fact that you get disconnected when joining a dungeon via duty finder, if the respective list is down, you can also conclude:
-the world interconnect is also handled by the very same login server

So, how to fix this entire mess:
JUST KICK AFK PLAYERS, that will reduce the load on the login server by 50-80%.
Why?
Well, because the number hammering the login just got cut in at least half. And that is what puts most stress on those servers