So here’s the situation - you are have two characters who, if you have access to them (i.e., the covers because the ISO will come over time) basically trump anything else you can do at their colors and rarity level.
What you’ve done is developed a crutch on two levels. One - people rely on these characters too much. They don’t try out other characters or spend as much time investing in them. Why would they? Thor or Rag are good enough to get you through most things. Two - the developers rely upon Rag’s OP-ness to be the “end-boss” for anytime they need a hard level. Instead of coming up with a villain devil dinosaur that is fun or interesting - instead you just say up Rag’s level to 240… now that’s hard!
Look through the forums here. Almost every ability in the game is compared to Thor and Rags red. Because they are so far ahead of the curve as to be game-altering and game-breaking. If a player knows about these characters and chooses to use something else, they are doing it in an attempt to salvage some fun while knowing they are not being as competitive as possible. Game balance is increased when you let players make choices that can be interesting but also competitive. Gameplay fun is increased when you don’t face a 85 Thor in 90% of the matches in a PVP or feel like you have to go through around round of converting reds to greens or reds to yellows. Rote, predictable, boring. If even a relatively low level Rags matches red in PVE, you know what comes next - cascade after cascade into death.
The devs have shown they care about this because of how they responded to Storm. And Thor and Rag can still be very powerful - just right now they are beyond anything. Make them weaker and make the other characters stronger. You can do both. Introduce new characters that are interesting and different enough from Thor/Rag that they create more dynamic gameplay. Feel free to create villains (countdown tiles or not) that are interesting and not just a boosted broken character. Be bold.