The thing about Rhea Dragoon is, if her aura activates, it gives her a shield, preventing her hp to be reduced further. Unless she is attacked multiple times within one turn, it's impossible for her to activate her aura more than once per turn. Moreover, she's melee, even during CF. In order for her aura to activate and make her hard to kill, 1. she has to be in the melee range to be able to hit her enemy. 2, the attack MUST not kill her. 3, the attack must not stun her.
Moreover, her CF makes her detaches herself from formation, meaning she won't be able to make full use of her aura unless she's in melee range and is fighting against mega boss or immovable unit.
I've been meeting several team with Rhea Dragoon on arena. Each time she jumped one of my squad member, she'll die next turn without being able to utilize her aura or CF on-attack skill due to being attacked by an atk talent Leon (plus AI somehow seems to always choose the same unit every single time I fought her). I imagine any other high attack unit can do the same. This is because she's still fairly squishy even after entering CF.
Also, about her CF on-attack skill refreshing herself, it is limited to 2 refreshes. Once she did the third manual attack and got out of CF, the refresh somehow got cancelled too.
There is also some problem when activating CF against non-mega boss type or non-immovable type enemies. It flung the target to a random tile, sometimes very far away from the point of origin. Sometimes making her waste her AP due to having to move to re-approach the enemy
Against mega-boss and immovable enemies, she won't even jump and simply enter CF (without dealing damage as it will be resisted by the target). This means she has to be on melee range before activating CF in order to make full use of it. Similar to Freya Berserker.
If anything, she's only winning in term of survivability and the quick availability of her burst damage. But her total dps will probably still sit slightly under Berserker Freya if the battle goes to the point when Freya is able to use her skill.
In my opinion, she's like a pierce hero version of berserker. With a bonus where she actually can be more durable than both normal Dragoon and Berserker. Her melee range and jump simply balanced her out.
She's good, I give you that. But not as good as the gladiator counterpart.