The way things right now, the 3/3 haggler and 3/3 socialite is about 1/10th as effective as the 5/5 however the socialite has the additional aspect that they continue to scale linearly with how many 5's they have in the 'primary' social skills. Someone with four 5's is about twice as good as someone with two etc.
That's just a consequence of how roll and keep works. The result of a given roll is roughly linear with the stats/skills used, once you have enough dice to consistently beat the difficulty, all additional bonuses just add linearly to your result.
For the 'base' difficulty of 15, that's about 3 dice. Haggling uses 20 which is about 4 dice and modeling uses diff 30 which is about 6 dice worth. That leaves a hypothetical 3/3 character with only 3, 2 and 0 dice remaining respectively for getting the result compared to the 5/5 who has 7/6/4
If you want to achieve something like what @brent suggests, the difficulty needs to be kept relatively low (like 10-15) in order to allow a 3/3 to actually beat it with some threshold. Then you can squeeze the high end by running the result through something like the power of 0.9. At that point 5/5 would still get about 2x the result of 3/3.