I’m not sure why people think it is some plot they had in giving free transfer to the largest servers. It wasn’t. It was a mistake they ended up making them more money. So they did a second time and purposely excluded those realms because people were paying to go there.
Even if they didn’t allow transfers to the biggest realms in that first free set. We would have just ended up with one of the medium pop realms of the time becoming a mega-realm instead.
The issue isn’t the transfers. It was not locking realms to control populations, and the refusal to merge realms when the balance was getting out of hand(If they even care about factions to begin with… I don’t think they do).