pretty sure we've been through this on this thread before.... let's go through it again
DXO is inconsistent and wrong. its no secret that that Sony has been using dual gain since A7RII but as you can see in your own the comparison you posted above, dxo doesn't even show it for A9 and A7RIV. but magically shows up on A9II which uses the same sensor and processor as A9.
Here's another example A7RII vs A99ii - sony themselves said its the same sensor and processor but somehow A99ii has lower dynamic range
View attachment 310283
have look on photonstophotos and you'll see its exactly the same and even shows the dual gain in operation at around ISO 640. A7RIV has a dual gain at around ISO400 which you can also see on photontophotos. What's more if you or anyone can be bothered you can follow the transparent methodology that photonstophotos uses and draw up your own graphs and end up at the same results. Bill's results has also been used and verified by many other tester like Jim Kasson, dpreview etc who spends a lot of time testing these things.
Is photonstophotos always correct? probably not... the results on there are based on RAWs contributed by the community and as such human error will play a part. Bill is completely honest about it. but its sure as hell more consistent and more reliable than anything dxo puts out at this point.