That's a bit of an exaggeration, unless you're talking about a racer car like a spec Miata or something. You'd have to go back pretty far to find GT racers that were slower than a modern production C7. Slick tires and far lighter weight make a massive difference, as I'm sure you know. I'd bet it's more like 40 years, and only when comparing to production-based racers, prototype cars would still be a great deal faster going back further.

If you want to do the legwork, I'm sure there are comparative times that can be found for the Nurburgring since it's been used for sportscar racing continuously going back just about forever despite minor course changes, and Corvette has surely tested there with the C7.

Still, the point that it is a wickedly fast car and they've improved it by huge margins compared to the C5 stands.

Edit: Checked. The C6 Z06 on competition tires did a 7:22 in 2012 at the Nordshleife. In '77 a Porsche 935 did a 7:31, but that was on a course about 2 kilometers longer than the one the Vette ran on, so you'd assume it'd be faster over the same distance by a good margin, even if we're talking about the C7.

Anyway, I just outed myself as a nitpicking ninny for getting so technical about that point. Sorry.