It’s for 3E/Pathfinder since that is what I play, but this may help with the alternate power sources and some drawbacks:
Basically Ceruleans are new and can’t hide spellcasting, Gray and Shadowcasters find themselves accidently drawing creatures into Athas as well as being hunted by a something from those planes. They’ll continue to use the older preserving and defiling methods because it takes awhile for them to be able to cast the same level spells with the different power source and sometimes the power source isn’t available. For preservers there isn’t much of an upside really to using an alternate power source, for defilers they wouldn’t be able to use defiler feats since those rely on destroying the environment. The primary benefactors are the defilers who don’t defile because they took that as a path to power, they defile because it’s all they know how to do.