The difference between 100% Eidolon and the ex-120% Eidolons is not great. Because if you want the ex-120% Eidolons to give you more than 100%, you'd need to use on-element sub-Eidolons. Which leads to slightly less damage output for slightly more damage output. Usually all that happens is that you swap useful actives for non-useful actives.
Hime are what make the difference. And Light gets some entirely fucked up Hime coming up.