DC writers more freedom to write their stories without any strict continuity, it was quite a mess in terms of constructing a coherent cosmology
The usual cosmology with multiple authors, there is nothing unusual or outstanding in this, but for some reason, this problem only applies to the DC universe. And I have never seen any compelling evidence or arguments why this should apply only to her, with the exception of repeated and cliched phrases about the logic and canonicity of another universe, in which there are also contradictions and illogical compositions. If you really want to try to lower the level of cosmology by specifically dividing cosmologies into different authors, then for starters, don't try to pretend that there are no contradictions in other multi-author universes.
Some of Morrison's ideas for Hypertime are now obsolete and most of them weren't even mentioned in the comics (or they were very vague mentions), although some still work well, but most have been abandoned.
This is a favorite theme of people trying to appeal that if something is not indicated in the cosmology of one author, then it does not exist in him. Bleed was not created in DC, and has not been mentioned in past comics, but has always existed as a construct in which universes float. Some of the Endless appeared in later comics, but they also always existed and existed from the very beginning of cosmology, Destiny appeared back in 1972, although Morpheus was invented later, does this deny the existence of Morpheus in parallel with Destiny? Of course not.The problem is not that there are contradictions, but a lack of understanding that the cosmological structure is revealed as more and more recent information is released. By the way, in TES, the entire cosmology as it is at the moment was also not initially thought out, they expanded and changed, which does not prevent it from being compiled into a cosmological level.
it would mean eliminating the works of certain authors like most old stories of Neil Gaiman, Mike Carey, DeMatteis and some others, since most of their information is outdated compared to current canon.
Has anything changed much? The heavens appeared and were shown on the map. Pralaya has also appeared in some comics. Lucifer also appeared in Crisis. The fact that a newer one replaced an old one does not in any way cancel the old one. Otherwise, we can throw out all the old appearances of Darkseid and Doomsday, because Darkseid was not previously listed as Platonic Evil, and Doomsday was not a multiversal parasite resurrecting himself in the higher dimensions?
And I also don't believe in the idea that every universe of the Orrery is a multiverse/continuity just because Neil Gaiman's Sandman was mentioned in Grant Morrison's Multiversity.
Sandman originally appeared in DC. Destiny appeared in 1972. Here you need to ask a counter question, who is more canonical, Dc, which created Vertigo characters, or Vetrigo, which uses Dc characters? Yahweh or his voice appeared in Pre-Crisis DC. Does this somehow contradict Vertigo? Or will there be some clear and normal evidence that Vertigo really has a different cosmology, different from Dc?
Edit: Of course, this is my personal opinion on the subject, but I feel like smaller composite cosmologies for DC, like Crisis Cosmology, would be a better idea than trying to create a "Frankenstein DC Cosmology" with every material and story and using headcanons or sources vaguely or not mentioned in the comics to try to reconcile the holes.
This is a problem with any multi-author work. DC is so far the only universe in which I have seen a division of cosmology, turning a blind eye to other universes with multiple authors.