They announced how worlds would be shuffled.

[Starflake]

O12 Clears per Server:
Chaos:221
Cerb:70
Louisaisuuax: 8
FrenchServer: 28
Omega: 7
Ragna: 108
---------------------

Light:186
Lich: 12
Odin: 57
Phoenix: 54
Shiva: 41
Zodiark: 22

____________________
Odin would rank fourth in Chaos for O12S clears. Great distribution. SE showing once again they are clueless. Also crafters will migrate to heavy raiding datacentres. Seems like SE really thought this through. Shocking stuff. Inexcusable.

[Fyce]

O12 Clears per Server:
Chaos:221
Cerb:70
Louisaisuuax: 8
FrenchServer: 28
Omega: 7
Ragna: 108
---------------------

Light:186
Lich: 12
Odin: 57
Phoenix: 54
Shiva: 41
Zodiark: 22

____________________
Odin would rank fourth in Chaos for O12S clears. Great distribution. SE showing once again they are clueless. Also crafters will migrate to heavy raiding datacentres. Seems like SE really thought this through. Shocking stuff. Inexcusable.

That's actually pretty balanced in terms of total clears. For Chaos, Cerberus and Ragnarok will likely push the other servers up in terms of clearing raids, as static recruitment will involve them more, and Light will remain quite stable.
Also, they probably took the languages into account when splitting, as it seems that Chaos will have more french players, while Light will have more german players. Not everything is about endgame raiding.