I don't have to be better than others with the noble background and 14 charisma.
You just need to be good enough to be relevant in the context of the campaign, really. That /is/ relative, though, in spite of BA making skill checks random enough that anyone who can make a chack can be relevant, once in a while.
So, if you try to make a character 'good at the social pillar,' and make noble background, as much CHA as the build can spare, maybe make even a specific race part of that, then swap in each of the various classes and what they bring to that pillar, you might, in a very well-balanced-in-that-pillar game, find that though each class is different, they each bring something equally valuable to the character. What you'd find in D&D is that of the dozen resultant builds, the one that swapped in fighter would be the worst at that social pillar - strictly so, I'd think in most cases (the Barbarian might give him a run for the bottom spot, it's pretty sad, too, that way). That's an imbalance. It's just a there in the mechanics of the game, nothing to do with who might be playing each of the resultant builds or what campaign they might be in....
...now, the beauty of DM Empowerment and spotlight balance is that the DM has tremendous latitude to compensate for an imbalance like that, if it even becomes an issue. (And it very easily might not. If only one player makes any attempt to engage with the social pillar, it won't matter how his 'build' competes with hypothetically optimal ones, only with the 8-CHA anti-social misfits he works with. 'Land of the blind...' and all.) That doesn't mean they don't exist, just that there's ways of coping with them other than mechanical fixes.