So you're saying that after playing the game for three years, rainbow is good?
Well, isn't that nice. Of course, you could've had more power 2.5 years ago.Your "efficiency" is wasting tons of resources over the years, just so that you don't "waste" some on non-SSR weapons which will stay nearly forever in your grid. You don't actually gain anything.
Also, why do those advantages only apply to a rainbowgrid? If survival is required, a monogrid user can just swap to rainbow and oh look. It's pretty much the exact same thing as what a rainbowgrid user would have for that specific Element. Because the difference between 49% and 56% is not very huge (as Character attack Eidolons count towards Assault), a monogrid user will almost be on equal footing in the rare cases where you actually need the damage reduction. Whileas the reverse is never true for rainbowgrid users - they can't just swap to mono and have the damage output.