As much as we want to see Cass Sin nerfed, but being a premium character, it's will be hard for devs to make that move. Because players who acquired her spent hard earned cash. Devs will be facing a decision whether to offend the few best paying customers or please the general population.
However, If I want to see a nerf from Cass, Her aura should be toned down. The 95% chance to trigger critical attack, not to mention trigger heal also is downright cheating already. That's the reason it makes her a very deadly combination with Rhea Glad. I believe 50% chance to trigger would be a more reasonable value. That's not even toughing the active skill yet. 3 CD is ridiculously fast for such an OP skill.
Because I thought it was futile to suggest for it's nerf, what I did instead was to campaign hard for the revamping of Valiants. I wanted to see them have a fighting chance against Dark Lord characters in arena. If not for the VF community pushing for a better improvement, devs would have made a useless revamp of Kiera. Devs did eventually accommodated some of our request, but only because of pressure from VF community. Yet, the overall Kiera revamp really was not enough. Kiera Elem is the only one that has the potential to make an impact in the arena scene. After that ordeal, I came doubt if devs still have a grasp of game balance or are they only basing their decision which will make the most profit.
I do agree that Kiera Ele became one of the best offensive mystics but I want to add that Kiera RM is also in a decent spot right now. While she cannot compete with her ele counterpart in terms of damage output, her bulkiness by mystic standards is one of the best, if not actually the best. Furthermore, her skill can push even all 3 guardians out of the center tile assuming you were successful in removing their resilience buff. Also, her skill hits all enemies regardless of their positioning and that will always be a convenient asset to have. It is also noteworthy that KieRM's skill oneshots most rangers not under the guise of SW's protection so while she can't do as much damage, she makes up for it with defense and utility while having enough damage to harm offensive heroes.
Back to topic, the valiants really should do the job of being able to at least counter DLs since the valiants and DLs are the main heroes of the game as protagonists and antagonists. I've been quite silent lately as I'm not getting my hopes up anymore for this game. Seeing as how it took months before the devs realized 'oh Kiera is so garbage she needs a buff' but to be fair to the devs, at least they did buff her. However, at this point in time,
most of the valiants are outclassed by the newer heroes. With Zhuge's introduction, I think WL suits a guardian team better than Kiera which is the squad she's most at home with. Additionally, Ele Zhuge offers impressive CC which can protect her ranger allies while further improving the offensive pressure that such a squad lineup can do. What I am hoping for is that valiants get reworked to specifically counter DLs since I think DLs will most likely be in the meta for as long as this game lasts. If a hero becomes meta-defining, heroes that do well against that hero/heroes specifically will most likely rise in usage to counter that said hero. Therefore, I think we can assume this game will really be called Valiant Force as the highest bracket will be a battlefield of DLs and Valiants should such a revamp occur. I hope valiants' revamp would not be wishful thinking on the players' part.