I think the problem with Charisma is that it can mean so many different things in DnD:
-Being naturally charming
-Being able to talk your way out of anything
-Being good at lying
-Being highly persuasive
-Being intimating/imposing/scary
-Being a good performer
-Being able to bend people to your will
-Being able to manipulate the weave
And it's hard to imagine a character would have ALL of those traits just because they have a high Charisma score.
The thing to remember though is that a racial bonus is not a guaranteed success, it's an increased probability. So a halfling is more likely to be seen as charismatic than another race for instance, but they could still fail their Charisma roll. In which case, the DM would say that their charms did not work on whoever they are talking to. So theoretically if the halfling is talking to a race that wouldn't necessarily find them cute, the DC would be higher.
