Kylo and Rey were very much equal opposites in the force. This could have been reflected in game in so many cool ways. They should have had the same release style, like Rey's hero journey being playable from both sides. They should have had equally powerful kits that were opposite in style.
I think we sort of... kind of got the latter portion, given that KRU's ability to soak up damage may be unrivaled, but Rey's healing immunity is the only one you see in top arena. The real problem is that Rey has a supporting cast that KRU just can't match. Without R2 it might have made sense, but R2 is in every team, and there is practically no way to even land a meaningful hit on the JTR, R2, BB8, OB, GK combo. You just take hacks at foresight until illuminated destiny goes off and they go nuts.
R2 remains the most broken thing in this game. He's even shoehorned into half of the nightsister teams i see for some reason. He's he reason the balance between KRU and Rey wasn't there, and he really needs to be a little more powerful i.e. uncleansable stun, to make them both viable arena choices.