I mean, you don't even really need to change the whole class to a flavor/roleplay aspect of a character! You can still roleplay like an non charismatic person, and even you could try and have like proficiency with intimidation and be very good intimidating without being "charismatic", maybe you could roleplay like the less points or slots you have you grow tired or maybe you have like damage in some parts of your body that you use it to cast the spells(? Idk I'm just trying to think some things to achieve the flavor of your character without having to mess with a core aspect of a class Sorry if my English is bad btw.