I’ll do a reverse reductio ad Hitlerum and say that a lot of people who had substantial enough communication with Hitler considered him very intelligent. Just, well, unhinged, with an itch he couldn’t scratch, with murderous overvalued ideas … But misjudgements usually used to justify calling him a corporal limited in perception are big because a man shouldn’t have such power, not because the particular man who had was dumber than the rest.