This foursome allows for a useful distinction among the physical abilities and among the mental abilities.
I would drop Wisdom. It attempts to be too much - perception, willpower, intuition, some knowledge - and it does trample on both Intelligence (some forms of knowledge, interpretive insight, etc.) and Charisma (willpower). The justification that Wisdom includes common sense is a strike against it rather than for it, since the idea that high wisdom characters demonstrate high common sense is laughable. I don't think that Intelligence and Wisdom are that different even when people cite the clueless professor or the like.If I where going to drop any mental ability score it would be Charisma. Intelligence is very different to wisdom.
You call that simplification? Your system has two ability scores! There should be ZERO ability scores. Beat that!Why not just simplify it even more and make it more elegant? Just use physical and mental for TWO abilites as you almost concluded but didn't quite make the jump--I even bolded it for ya.