Neftis is limited. Aether functions similar to Titania and pairs well with Shingen. Isis functions similarly to Gaia but her Cover has a duration of 5T and doesn't make her invulnerable, meaning that powerful attacks can wear her down. She also has no AoE mitigate. She's basically a weaker Gaia.

Aether could sub in for Gaia for a Burst build instead of Titania. But she wouldn't be available until the 5th Miracle ticket, so that's beyond the scope of current planning.