Re: Ignoring Superman 3 and 4
I looked at SR as an alternate reality or alternate timeline to STM and SII. I think thats what Singer was trying to say without getting too Complicated. Where events similar to those films happened before SR but they also happened a bit differently. For one thing the main crystal at the fortress isn't green like in the Donner material.
I felt Birds of Prey did something similar with the Batman films being used as story inspiration even though there are differences in continuity. More differences than there are between STM/SII and SR.
Basicslly I like to see it as a film versions of a multiverse. But that's parts just fannon.