Not true. That's one of the points Cerny missed to address. The XSX can use 10Gbytes of ram at 560 GB/s. That is the obvious place where textures, frame buffers and all the key stuff is allocated. The compiler/linker will make sure of that, all games, all the time. The PS4 only has 448GB/s. If 448 GB/s is enough for safe 4k/60Hz I'm really not sure. The games wil tell, but I think this is a gamble (simply for using lower priced ram chips) that might not pay off in the end. On the same games, the XSX will have more (native) pixels on screen. On the other hand, the PS5 will have the "better" pixels if all the ssd-tricks are used.
But 10 GB of texture frame buffers and all the key stuff will not suffice , if PS5 run the same number, they can allocate more ram for those effect because the memory module setup are unified and running the same speed.