I know you don't care for the GBA script (I adore it myself ) but I honestly feel the only real difference in either translation is clarity of the characters themselves. I honestly feel Kefka is a smug narcissistic sociopath in the SNES translation but of anything, its bogged down by a bad translation that makes Kefka more comical than threatening. Even in the lines you quoted, I don't see Kefka really making a statement of hating humanity as much as revealing he doesn't care about their existence (sociopathic tendency).

I stated before that Kefka reveals more of a nihilistic view of humanity by end game (same in the SNES) so your statement of the difference between both versions of him is moot cause your judging one by his end game persona and the other by his opening persona but at the end of the day they are basically the same person. I feel the only real difference between the two versions is that one translation makes Kefka laughable and the other makes him seem more like an evil twisted human being from the get go. It's all about interpretation and somehow, I just don't think either of us are going to ever see eye to eye on this subject...