I think street smarts go further than book smarts for the average wiseguy.The annals of Mob lore are full of men who if given an IQ test,would score at the borderline retarded level.
As to Galante,he may have had the mental age of a child,but in areas of his business,he was a Nobel Laureate.
It is possible that Galante,if tested, might have scored low as far as mental age,but this could be attributed to incomplete formal education,cultural differences,etc.