That chart deliberately leaves out UHS-II and UHS-III, to make SD Express look miles better than existing standards. I support SD Express but that is just sad.
the new SD Express specification is also backward compatible with the legacy UHS-I interface.
Yes, with a "but". If you stick a NEW SD Express Platinum Turbo card in a UHS-II or UHS-III device... it will run at UHS-I speeds. This makes perfect sense given their desire for backwards compatibility, as they have to use the UHS-II/III pins for the PCIe link and keep the legacy (UHS-I and older SD) pins intact for backwards compat. However it is a bit counter-intuitive for the average person. They may not understand that a "faster" SD Express card is actually slower in a UHS-II/III device than a "slower" UHS-II/III card.
Also backwards compatibility isn't guaranteed, especially as capacities increase. But by that point we should all pretty much be on the new interface or perhaps even a successor. SDE-II... repurpose the legacy pins for another lane?