As more and more champs come to the game the harder it'll be to keep a balance but we have had ic say why they did not do a major champ balance this last patch and that is so they can test the Artifact changes.
Champion that will be buffed even if slightly are batman, robin, nightmare batman.
Gas cat is not broken powerful but yes. I think I found the area where she needs tweek to better balance with other champs. Now will it happen? Idk.
Also Sinestro will be nerfed/buffed. Skill will have more range. Health % based damaged will be reduced and power based damaged will be buffed.
Now these are all maybes as they are doing constant testing on these champs and watching results of what power dish out.
I hope this can help your balancing issues.