Congestion is artificially made as well to help stagger logins, if we're referring to how every server still makes you wait to log in. Even Dynamis has it and we all know they're on their last leg atm in terms of population.
If you mean server locking, it's accurate that Balmung has always just had a higher population because it's the main RP/ERP hub in Crystal. They've been shut down for over 6m now because people spam transfers there when they do open and pack the place (I'm of the mind that it's something of a status symbol amongst some of the RP community to live on Balmung). You'll see the other DCs shuffle servers around as normal.