Itachi's intelligence is over rated. When it's said that he was as smart as a hokage at age 13, he's being talked up to make Sasuke feel better. And look at all the hokage, they're not stupid, but they're not exactly military geniuses either. I'm not saying he isn't smart, but he doesn't show an intelligence surpassing or honestly even equalling Shikimaru's or his fathers.
Itachi's real strength isn't intelligence, it's perception. He has an incredible ability to predict the actions of people whose personalities he understands as well as a solid understanding of human nature. It's an incredibly useful ability, but calling it unrivaled intelligence is inaccurate and misleading.
