I agree that the Corvette is a whole lot lighter, but the statement was that the Challenger Hellcat is the fastest American muscle car. Regardless of the reasons why, it is not faster than a Corvette, and if if it should get faster I'll bet that it will not take long to bump up the Vette.
My sister just took her 2014 vet on a road trip, averaged 34 MPG over about 1200 miles. Not bad for 400+ HP available.
Heck at 4300 lbs that is getting close to the weight of a full size pickup at 4700 lbs.