If being competitive is a matter of adding more numbers to your profile and/or going Super Saiyan then I wouldn't say they're overpowered. They may be out of scale for a given situation but terms like OP imply there's something inherently wrong with the character which isn't the case. She just needs to find someone who can keep up with her.
This RP allows for a range of characters, between T1 and T8 by my reckoning of the old system. So far, the majority of characters have sat between T3-T6 which is fairly average and standard. Corban and Blythe are both solid T7-8's and therefore quite objectively -overpowered- as in significantly stronger than the average character submission. Do stronger characters exist in the fragments of people's minds and other settings, sure, but within the boundaries of this setting they are literally some of the strongest characters you can actually enter.
Therefore, they are going to be hard to find fights with, for varying reasons but mostly because they're overpowered in this setting, due to the average character submission.
The ironic thing is that the two strongest characters probably couldn't even fight eachother, for the reasons I mentioned earlier, it would require Divinity to no-sell, because Corban lacks the tankiness required to actually weather one of Blythe's attacks, where-as Blythe can both tank and regenerate his.
Point being, Blythe is cool and all, but considering we're barely getting anywhere as is entering this setting with the strongest possible character probably isn't going to get you a fight anytime soon.
In regards to other things, I noticed Xiomara has a blanket immunity to the weather, which is technically not allowed in Arena but also hilarious. What does being immune to the weather entail? Immunity to being struck by lightning?