I think you and I are in furious agreement (not sure if you meant to reply to me or the GP).
If the "C" guy does everything then he's not specializing in a single task. He's doing two tasks, the C task and SQL task. Similarly if two "C" guys do the whole thing they're still doing half of two different task. But if you put the "C" guy and "SQL" guy together, now each of them can do one thing, and one thing only, and the whole job gets done faster.
Now, has the group performed more work than the "sum of the individual contributors". I would say hell yes (as you illustrate, the same job gets done in 10 man hours vs 25). However the argument that the GP was making (or at least what I understood him to be saying) was that if we define the output of group to be "the sum of the amount contributed to the group by each individual member of the group" then the output of the group can't be greater then the sum of the individual members of the group. Now to me this seems like a meaningless tautology, so I'm not sure why he would bring it up, but I suppose that it's factually true. Of course it's entirely possible that I've completely misconstrued what he was trying to say.