Well it says that "Louisoix summons the last of his strength to call upon Althyk, the Keeper, god of space and time, to send those surviving heroes into an aetherial rift" which makes me think that he didn't use any of his strength to do it but Althyk made the decision to. Seeing how the gods couldn't stop Bahamut and was under threat of the Garlean empire, that Althyk only had the strength to keep the heroes safe since somebody who's being saved wouldn't really want to struggle with the spell.