I've been playing on ranked arena and every so often I go up against someone whose life bar barely moves. I've noticed it mainly from oppents on the Kaia server. I will get 2 big hits in but it seems like I didn't do anything.

Lol there is no hack. They are just more powerful than you. Even if theyre around the same level as you, they can wipe you as fast or faster compared to someone who is a lot higher in level/skill than you. Character Power (CP) is King here...not levels.

Check your:

CP
Skill

Im at 7276 cp I've gone against people who have 500 less cp and still do good damage. So the person must have like 8000 cp.