Just spent some time compiling this chart, and its actually changed my view of things.
It looks to me like the only outlying card really, was the 2080 Ti. The rest of the cards actually form a consistent and fairly reasonable price to performance pattern and the improvements between series (especially for Nvidia) are clearly visible.
Firstly the Nvidia Pascal series is very linear in pricing, and actually if you project that green line forward you get exactly to where the 2080 Ti is in terms of pricing and performance.
Then Turing (the dark green line) is again reasonably linear with the exception of the 2080 Ti. The remaining cards follow a similar profile to Pascal except shifted to the right. This means they have delivered an increase in performance at broadly the same price points.
Taking a look at AMD, their RDNA1 series could effectively be an extension of the Turing series line at the lower end.
The Vega and Radeon VII cards in the AMD GCN series are clearly sitting between Pascal and Turing both in price and performance, so it looks to be spot on in terms of placement, representing an improvement over Pascal but not getting to the level of Turing.
And the weaker GCN RX cards are also sitting, comparatively speaking, in what looks to be the right place in terms of their price and performance.
* I did my best to find the dollar release prices of all the cards but there was some variability in the data sources so they might be slightly off.