Pretty sure the base/ra/ga/ja is how they always were in Final Fantasy games, but you got limited space in English. For examle FF4 you can only fit 5 letters in there and even 'Boltaga' would be too long, let along 'Thundaga'. As pointed out there's no inherent meaning to these suffixes though it's also problematic with numbers, like you'd think Fire 2 is better than Fire 1, but they're not even the same type of spell (AE versus single target). Honestly it'd have made more sense just to have unique names.