So with the last moments of the Balthier event I retried the Judge Gish Elite battle, mainly for Waterja.
Personally, this is a major breakthrough for me! I've never been able to complete the last boss of any kind of event going back to Rinoa's Event (did not even try T-Rex Elite). I do not own Phoenix, Valefor, Waterja, Firaja, Leviathan etc. nor any reward for finishing (not even mastering, ha) any last Elite boss.
Today Waterja is mine

And I can hone it already! I hope it will be useful for the Cecil event because I need that Firaja... (only 2 final Elite Stages left with Scarmiglione (I will use FIRAGA on that bitch) and Dark Cecil).