She's only a threat if you can't kill her in a single turn. Her shield doesn't activate for herself if she's dealt lethal damage so she's most probably dead after she jumps in.
Unless u are playing a tank team with no damage, then gg.
- Airk of Infinity
And how many can do that? I think there's only a handful of players with super duper deadly archer squads that can kill rhea in turn 1 (specially those rhea guarded at the backrows). On the other hand, squds with rhea are proliferating.
- Ferico of Pluto
As Airk said, if you can kill Rhea Dragoon in a single attack, she won't be that much of a problem. You don't really have to kill her at turn 1. It's easier to do so after she jumped away to you.
Personally, I've been killing Rhea Dragoon with Leon built for SDD in my tank team or my other arena team. Rhea always target the hero with the lowest def. So it's actually quite easy to deal with her. Especially since my lowest def unit is usually placed within Leon's melee range.
Rhea Gladiator is another case altogether. She's weak if placed on front line, since she'll most likely use her turn to walk forward. But if placed on the back, or if given the chance to cast her CF, paired with archer, she's hell more annoying. Since she can stun most if not all squad members in a single attack, not giving us any chance to act even if we survive the archers attack trigger.
On my opinion, Rhea Glad is actually the one that has to be killed as fast as possible. But with some smart squad placement on the opponent side, it's almost impossible to do without using archers.