I have heard this sentiment before, and unfortunately I am not convinced that the obnoxiousness of this character was intentional rather than accidental. I don't have much to back this up: basically my hypothesis is that Sanderson is trying to pander to a specific audience, to whom the witty banter he is attempting is appealing, and genuinely attempting to make Shallan 'cool' fits with this hypothesis. Furthermore, as others have also mentioned here, his other attempts at similarly witty characters have also been flawed, so there's that.