2014 Corvette Z51 Stingray weight versus 2013 Corvette Grand Sport-where did things go wrong?

By all accounts, the current Stingray equipped with Z51 option should be lighter than the previous Corvette C6 Grand Sport coupe equipped with manual transmission.  Why?

Because the last Grand Sport M6 was equipped with dry sump system while being wider and using the "obsolete" steel frame.  The last Grand Sport also had wider and heavier tires than the current "track ready" Z51 Stingray.

So what give here, considering than in spite of Stingray's quintessential mouthpiece, +Tadge Juechter assurance regarding the new light weight frame and such progress made since the last generation, the new equivalent of the obsolete Grand Sport weighs over 130 pounds more.

This is of course a rhetorical question since Juechter does not have a logical explanation available, at least not one that could make the new Stingray look good.  Tough luck Tadge, huh?