The Legendary Vault dwellers are based on their series counterparts and there is no stereotyping there. The highest base intelligence belongs to 4 characters: 3 males and 1 female. The disproportion there has to deal with the characters used in the actual games. Just a side note, the lowest Legendary Dweller intelligence belongs to Jericho (a male).
The generic ones are random (except for being born, in that case it's somewhat based on parents). These dwellers start with 12-13 stats that are randomly distributed and only the dwellers born in your vault might have a stat that has 3. The only other dwellers that are different are the first few you get because they will be your anchor for the first 3 rooms where you get one dweller with High Strength, a scond with High Agility, and a third with High Perception. Their gender is also random. So if there is an issue with your dweller offspring having low intelligence, it might have something to do with who you are breeding. If the randoms that appear at your vault have low intelligence, it's just random. 99% of the randoms that join your vault from the Wasteland either have 1 or a 2 in the stats, and offspring can get up to 3. If the random wastelanders that join your vault have low intelligence, that is just random. I wanted to breed some 3 Int dwellers but couldn't because all my dwellers had 1 intelligence. It's luck of the draw there, just like the random loot in the lunchboxes. Sometimes all you get is clothing, other times your first lunchbox contains a MIRV.
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