That is a fair point, about not wanting each character to be able to master a dialogue skill. There are a few ideas about how to mitigate the effects of dialogue stats. I don't have any magic bullets, just some stray thoughts.
I still think trying to take all the associated stats and trying to shoehorn them into one of Charm, Intimidate, or Reason might be the wrong approach. Larian had a different idea for those personality stats, and redesigning them to also work for that might be trying to fit an oval peg in a square hole.
