Also can I just say, and I know this isn’t any logical argument, but Eonar is just boring.
Everything about Elune is so much more interesting than the only female Titan who becomes the macguffin for a patch and then goes back into irrelevance once the patch is over.
For at least the short term, the Titans and the Legion are dealt with. Perhaps one day they’ll bring them back, but randomly introducing this idea of a ‘sister’ of the Winter Queen and then tying it to Eonar, who has no relevance in the story whatsoever, seems shoddy and confusing storytelling. Because even if Eonar IS the sister, what does that matter? Eonar is locked away with the rest of the Pantheon imprisoning Sargeras, unable to be involved in whatever is going on currently in the story.
Elune is already involved in the Shadowlands through Ysera, Tyrande, and the Night Warrior couple, so she’s thematically appropriate to fill that role, even if you ignore all the other arguments I made earlier.
Honestly we just need a conversation between Tyrande and the Winter Queen and I think we’ll see who the sister really is.