Much of my concern stems from the difficulty most everyone has trying to roleplay a low Int/Wis/Cha score when there aren't mechanical limitations built into the system. Deciding exactly what someone with a low Int but high Wis is capable of thinking/doing in or out of combat is not something I want to be troubled by around the game table, however that shouldn't be ignored either when someone gains a significant mechanical advantage in the form of better physical stats they enjoy every combat.
Well, with the current point buy, only one of these stats can be below 10, and not that far below either (8 isn't mungostupid if it's Intellegence, for example, it's just a little slow.) So in reality, you're playing characters with average levels of mental capacity at worst, which is a lot easier to envision with a single trait that excells.
Average Intellegence and Charisma, but High Wisdom indicates someone who is perceptive, but perhaps they are quiet and don't try to reason what they perceive means. They might notice the smudge on someone's shoe and that they're acting a bit nervous, but they aren't Sherlock Holmes and can't deduce the culprit's been in the garden.
Average Charisma and Wisdom, but High Intellegence means they're more likely to stand back, go with the crowd, and spend more time thinking than talking. They won't notice the smudge, but if the above guy quietly tells them, they'll be able to say 'Yeah. Probably was in the garden or something.' But they'd be less able to persue the matter or convince someone on its importance.
Average Intellegence and Wisdom, but High Charisma is just smart and perceptive enough to be convinced as to the value of the above information, and while they won't be able to add to the hypothesis, they'll be the most capable of confronting the villain in this case, and force a confession out of them through sheer force of personality, be that through a clever verbal trap, or outright intimidation.
You're not dealing with mungo stupid. All three characters are smart and perceptive enough to understand what's going on once someone points it out, and all three can communicate to whoever it needs communicating to. They're average except for their individual talent that sets them apart as individuals.
When dealing with the 10/10/16 style mental attributes, ask yourself what sort of personality does the character portray, and play the 10s as average. Sub-optimal in terms of being an attack-stat is not the same as sub-optimal on the bell curve of humanity.
