Output of the Sugar & Sulfuric Acid Reaction?
The product is not pure elemental carbon, but instead an amorphous solid that consists of mostly carbon atoms, with at least 5-10% of the atoms being other elements.  For example, one academic paper from 2001 found that the "carbon" formed by sulfuric acid catalyzed dehydration of sugar had a $\ce{C}:\ce{H}$ molar ratio of 14:1.

Such materials are sometimes called hydrogenated amorphous carbon.