SG Zoe Should Have Been the Legendary
With all the lore surrounding the new skins, it seems like Zoe is either the main villain or one of the main villains in the established Star Guardian universe. The idea of her skin is amazing and visually it's appealing and creative. She fits perfectly for this role. If she's had past fights with other guardians, caused corruption, and generally desires to corrupt or kill all of them, dialogue expressing that from her side would have been pretty neat. Zoe, more than likely, has a lot of stuff to say.
Xayah and Rakan don't get a lot of extra added depth from making them legendaries. Xayah is just Xayah with a few extra lore lines thrown in and Rakan gains absolutely nothing subsistence wise out of his voice lines aside from being the equivalent of a flamboyant disney villain.
All other villains from established universes have gotten legendaries (Thresh, Kayn, Zed, Veigar), just feels bad that the one antagonist we have for one of Riot's most popular skin lines got cheated out of what could have been something extremely interesting.