Kylo Ren can be a crutch to your arena team now especially as more Yoda's enter the pool of characters people have... As Yoda can potentially give his whole team retribution... and most people are super annoyed by counter attackers (e.g. Dooku)... Last thing anyone wants is to fight a team full of people who can counter attack every hit they take!
IMO ..the only time a person should use Kylo Ren in the Arena is when they have a FULL First Order team led by Phasma. Running such a team you'll understand why Kylo Ren's damage isn't any higher than it is currently.. and do not be surprised at how devastating a FULL FO team is... What surprises me is so few people actually use a full FO team!