Being smarter should give higher base INT in a logical sense, but in regular board RPG, stats are mostly for either checks or unlocking skills, and they don't affect your choices, rather, they just affect your success.
For example, Maki was the smartest by far, leading her to a much higher base INT stat.
Kokoa, on the other hand, has the highest total INT stat, meaning she can pass INT checks with ease. But because she's an idiot, she will never attempt an action that requires such a check.
Just my 2 cents on the matter, though it's possible the author has other plans/never bothered in the first place.