The grandposter actually doesn't say "social skills" are worthless. You're kinda putting words into their mouth. They only claim that that type of interview is biased for one factor.
"Culture fit" is one of those things that seems to be used as a proxy for traits that are illegal to take into consideration during the hiring process.
At its worst case, sure. But it also means, can I work with this person? Can we be productive together? Are they picking up what I and the rest of the team will be throwing down?
Everyone has had to do a terrible group project in school where the group dynamic was just not there and the whole thing suffered, despite all the smarts being at the table. This is to attempt to avoid that exact same thing from happening, because often you just don't have the time to flub around telling someone how to document something properly for the 10th time.