Where do you get that info?
Extrapolation from the Quadro RTX 5000 specs.
If the GeForce RTX 2080 is a fully enabled GT104 with modestly higher clocks than the Quadro part, it will have very similar shader performance, moderately worse pixel/texture fill rate, and slightly worse memory bandwidth than a GTX 1080 Ti. Assuming there are modest enhancements that allow it to do more work per-clock per-functional unit, it should be faster than a 1080 Ti, but not by much.
Because during the presentation, Jensen highlighted that the computing advantage will be there in 'legacy' rendering as well. I.e. day 1 advantage, and a significant one.
He's talking architectures, specifically the big die parts of each. That's GP100/102 vs. GT100/102, where the new part is 40-50% faster than the old one. The Quadro RTX 8000/6000 will be much faster than the P6000, and the RTX Titan or RTX 2080 Ti will be much faster than the Titan Xp or 1080 Ti.
However, the RTX 2080 is a GT104 part...it's to Turing as the non-Ti 1080 was to pascal.
NVIDIA has zero competition currently and has spent a large portion of their transistor budget on Tensor and RT cores that are going to do exactly nothing in 99.9% of games upon the release of the RTX 2080, so the bar they have to hit is not high. If it's
any faster than the 1080 Ti in 'legacy' rendering, they'll be successful.
This is the perfect time for NVIDIA to push raytracing. If they had to face a credible competitor architecture from AMD (and/or Intel soon enough) they'd almost certainly have fallen behind in such legacy apps, but with no such competitor, they barely have to improve over their own extant parts with the initial launch.
The GTX 1080 was quite a bit faster than the 980 Ti, but Pascal was a straight upgrade over Maxwell 2, had much higher clocks than previous parts, and didn't spend any transistors on new features that couldn't be leveraged in existing games.
The GTX 980 was often only slightly faster than the GTX 780 Ti, and I think that sort of improvement is a more reasonable expectation with the RTX 2080 over the 1080 Ti, at least for legacy apps. Newer DX12 DRX apps, especially ones using NVIDIA's GameWorks RTX will either be much faster on Turning or flatly won't be able to use all of their features on older archs...however, broad adoption, if it ever happens, is likely to take some time.