A320: Why do SDACs supply all three DMCs?
The Hydraulic System is displayed only on the lower ECAM which is supplied by the DMC2. Nothing about the hydraulic system is shown on the upper ECAM supplied by the DMC1.


That is not true. If DMC1 or DMC2 fails, DMC3 takes over. But if the display fails, the other display takes over. So the hydraulics page can be displayed on the upper display. It can even be displayed instead of the MFD or even PFD if both ECAM displays fail. Similarly for all the other ECAM pages.