Yes, the "gap" referenced is a new flagship vs last generation's flagship. No, the conclusion in this review is not warranted by the data. It's straight up nonsense that only makes sense if you let Nvidia's marketing department dictate how you evaluate their "generations" of GPUs.
Here are the actual "generations" of Nvidia GPUs, by architecture:
Fermi (GTX 4xx and 5xx)
Kepler (GTX 6xx and 7xx)
Maxwell (GTX 9xx)
Pascal (GTX 10xx)
Turing (RTX 20xx)
Ampere (RTX 30xx)
Ada (RTX 40xx)
Using any other criteria to determine a "generation" of GPU is ignorant and misleading. When one speaks of "generations" of graphics cards, one speaks of GPU architectures, not specific SKUs.
And here are the performance jumps from the top flagship card in each generation to the next, based on TPU's own data:
Tesla 2.0 (GTX 285) --> Fermi (GTX 580) =
67% performance jump gen on gen
Fermi (GTX 580) --> Kepler (GTX 780 Ti) = 1
04% performance jump gen on gen
Kepler (GTX 780 Ti) --> Maxwell (Titan X) =
45% performance jump gen on gen
Maxwell (Titan X) --> Pascal (Titan Xp) =
72% performance jump gen on gen [Titan Xp and 1080 Ti were very similar, 1080 Ti a couple points faster]
Pascal (GTX 1080 Ti/Titan Xp) --> Turing (RTX 2080 Ti) =
39% performance jump gen on gen
Turing (RTX 2080 Ti) --> Ampere (RTX 3090 Ti) =
56% performance jump gen on gen
Ampere (RTX 3090 Ti) --> Ada (RTX 4090) =
45% performance jump gen on gen
If you assume the "true" Ada flagship will be a 4090 Ti, and that card will be 10% faster than the 4090, then Ada is a 59% performance jump gen on gen.
In no way is this remarkable. It's decidedly
unremarkable. Ordinary. Expected. Typical.
If you exclude Kepler, which WAS extraordinary and remarkable, the average gen on gen performance jump is 54% per generation.