Hey man, just so you know, I'm not trying to start any fights here, just enlighten. I have a lot of experience doing GPU performance profiling. And I have experienced the power difference between essentially every GPU on the market. I can tell you straight up, that while most casual users probably won't be able to tell the difference (and likely wouldn't have been able to tell the difference between thier PS4 Pro and X1X), that even the 20% difference between these two cards will be very noticable on many titles.
To give you an example of what I mean, we can use PC GPU performance profiling as an example. On the website passmark, a sub-20% difference essentially gives us (and correct me if my math is wrong) the difference between an RTX 2080 and a 2070.
Video Card Benchmarks - Over 1,000,000 Video Cards and 3,900 Models Benchmarked and compared in graph form - This page contains a graph which includes benchmark results for high end Video Cards - such as recently released ATI and nVidia video cards using the PCI-Express standard.
www.videocardbenchmark.net
RTX 2080 - 19371
RTX 2070 - 16615
We can look at any number of game benchmarks between these two, and immediately see performance differences (feel free to pick any PC game on the market and try this out).
Take Gears 5 as an example:
An enlarged full size image from https://www.tweaktown.com content.
www.tweaktown.com
..
At 1080p (fps)
RTX 2080
Avg - 125
Min - 98
RTX 2070
Avg - 98
Min - 76
At 1440p (fps)
RTX 2080
Avg - 89
Min - 72
RTX 2070
Avg - 71
Min - 57
At 4k (fps)
RTX 2080
Avg - 51
Min - 43
RTX 2070
Avg - 40
Min - 33
If you feel the difference shown above won't make a difference to you, then fair enough, and all the power to you. In this coming generation though, I'm assuming we are going to see developers target all three of these scenarios, sometimes on a regular basis.
As you can see, the difference seems greater as the resolution goes down. For games that target 120fps at 1080p or 1440p (this could be a popular choice when using resolution scaling), PS5 will need to make up for a significant performance difference by adjusting graphical settings, tweaking resolution, whatever developers can do.
Another way you could also measure this is perhaps by comparing graphic presets between RTX 2070 and 2080 on games that do that well (Gears 5 once again does that incredibly well), to see how developers tend to prioritize visual settings to make the most out of a GPU.