I'm afraid to say, you're letting your emotions about the creators of this game get to your perception of the story. It's not real world. The creators probably chose Earth not because "Wee, Lightning is now in France brb tickets" but because "What's an easy to understand image of a world that's as un-fantastic and humanistic as possible? Well, Earth." There were JRPGs in the past that used this story device. Retcons... eh. I wouldn't say the original game's writing was waterproof either.
You are very much right here Frumix. That's the interpretation they were going for.