It appears that with persuasion it is less about the stat in brackets and more about the type of response. Certain NPCs respond better to certain types of responses. A rogue may respond better to strength/wit than intel. Someone with an army at their back likely won't be persuaded by a STR check.
I had Sebille in my party and my main char had skilled Persuasion since the start and I didn't have to fight him at all.
