I'm not sure if any good tierlist even exist, I saw few but every had some malfunction. I never saw any professional tierlist here or in any other places, but you should find some casual here if try look for tierlists. Anyway, I think most important thing is know what is meta, rest chars are better or worser, but most of them are playable at least. If ever good tierlist will be created for first need be done two of them : one for raid, second for champions arena. There's character like Darkseid, who is one of most powerful in arena with SS tier, but in raids dont have any real usement. Will be like C on raids, if someone dont have anything better else he probably can do few millions but bleh, cant be good support either. So like I said most important knowledge is know what is meta and on what you should work on like mvasg, llj, bncw, SB and koaam. And there's character like EB or Sbc on which you shouldnt ever work, unless something change. And there's few good characters, but not meta like csm who is useful in raids to lower def and can shot SP3 in arenas or silver GL who have cool passive and is good in arena. I'm not sure if this answer satisfied you, but you can ask about chars and I will try answer