Was bullshit!
While Light Nike is stronger than on-element Hime, the actual number is lower. Around 14% is more correct - still a substantial upgrade over any on-element Hime, but not quite P2W Eidolon level.
So, let's go over that 14%.
Light Nike brings 180% Assault to 300% Assault, so 4 (100% base + Light Nike's buff + weapons) / 2.8 (100% base + weapons) = ~1.428
Because we can disregard Light Nike doing ANY damage off-element, you have 4 Hime (well, 3 Hime + Soul) dealing damage. So 4 Hime * 1.428 = 5.714 damage output.
5.714 / 5 (which would be the normal amount of damage you'd get with five on-element Hime) = 1.142
Thus, ~14% increase. Of course, we have to remember that at the very earliest, this applies on turn 11. Content doesn't take you that long? Don't bring Light Nike.
Of course, this number can be mathematically challenged fairly easily. For example, this calculation entirely ignores damage caps (pre-Light Nike 700k burst hitters would hit damage cap with Light Nike) or damage skills used by the potential fifth party member. Please do challenge it - I'd love to go through the subject more thoroughly.