The first thought I have is that it is basically the same car as the Beetle. So why again is the Beetle a C car?

The MkIV chassis is not a huge advancement over the previous generations. It still has mac strut front, twist beam rear, bad camber curves and an instant roll center that moves too low if you lower it too much.

The unibody is a bit stiffer than the MkIII.

The motors are not significantly better IMO.

The brakes are better.