It's more of a nature in the game that it's real grindy. My luck is pretty rotten in all gacha games so I can't say much. But FKG in a way, is pretty merciless too without at least 1 guarantee gold per 10 draws. (It has bonus as 10+1, but 'legendary draw' exist along with it) It just that the game is pretty easy to farm event girls and they are perfectly capable to clear events even with generally inferior stat. Rainbow may be needed for super high-end difficult stage, but it's not world breaking if you can't get one.