You're wrong and you'd know this if you actually did any testing at all. Even with rainbow, there's quite a big difference between using x2 character, x2 element, and a character/element mix. x2 character provides the least amount of extra damage, x2 element is roughly the same or slightly better--depending on the eidolon and grid assault bonus, and character/element mix is by far the best increase in damage.
Last edited by BakaHentai; 12-22-2017 at 11:17 AM.