I wouldn't rate "unintelligent" as a superlative, since there are varying degrees of the condition. A person with an IQ of 70 might be said to be unintelligent, while one with an IQ of 50 could be said to be less unintelligent than one with an IQ of 70. The former, then, could be said to be unintelligent, while the latter could be said to be very unintelligent.
...while one with an IQ of 50 could be said to be less unintelligent than one with an IQ of 70.”
Wouldn’t a person with an IQ of 50 be MORE unintelligent [less knowledgeable] than one with an IQ of 70?