Transfer to congested servers.

[Stillwaters]

This is hyperbolic nonsense. According to the most recent unofficial census Balmung has just shy of 22,000 active characters. Levi and Cactuar come second and third respectively at almost 17,000 each. The gap has closed tremendously. In fact, Gilgamesh isn't even top three in terms of active characters now. Both will unlock soon enough, though probably not before 2018.

Cactuar is fourth, behind Omega as well as Leviathan.

Difference is actual active population, not characters created. The census counts any character that has any change (achievements, mounts, level) count toward active players, but not ones that consistently play. Only Omega has closed due to active player numbers reaching the same as the other congested servers. One can assume that Cactuar has not reached the same amount of active players as Gilgamesh, despite having a higher population count.