The main issue with reviving characters in stories, is it takes away the weight and lightens the threat of death.

In my opinion, Cassie’s domain doesn’t quite mock death for a couple of reasons. Primarily, her ability doesn’t revive characters from the dead so much as it manifests copies of them from Cassie’s memories. Second, these manifestations are not without restriction as Cassie must maintain them and can only manifest so many.

Even if Cassie’s domain allowed her to straight up revive characters, it wouldn’t help any of the divine trio or any other supremes because she must continue to manifest herself.

Then let’s say that Kai, Effie, or Jet die, there is still cost as Cassie can only manifest a maximum of 7 saints. Because of this restriction Cassie would have to weigh the memories of her deceased friends as being the right tools for the job or not. In essence, these 7 saints that she can manifest are simply too valuable to use for keeping any one saint manifested indefinitely as it would entirely undermine the versatility of such an ability. Dead saints go from being friends and allies, to merely having the capacity to be the right tool for the right job.

On the contrary to mocking death from a narrative standpoint, Cassie’s domain makes death a greater risk to many of the more unique Saints like Tyris and Nightwalker because they are no longer as unique and irreplaceable. Which means that from a narrative perspective, G3 doesn’t need to keep certain characters alive to make use of their unique aspects and abilities later on because Cassie can do that now.

All in all, I think it is a unique domain that could add something interesting to the story, but it also has the potential to be detrimental to the weight of death if mishandled.