Definitely not happening. But more importantly, you really shouldn't be spending resources on a team that is only able to do 6-7M. A properly tuned team will do far more damage than that, without needing great stats.

I doubt there is any mechanic in play that is reducing your damage to get you to buy more keys. Even if Plarium was going to do something like this I don't see them doing something as blatent as cutting your damage in half. Something like that is way too noticable and easy to expose. 

I would start by looking at the gear you have on your CB team to ensure that something isn't missing or hasn't been swapped then look at anything else you may have changed w/o realizing it such as masteries. 

Second, I personally wouldn't waste real money on keys unless you just want to. The problem you are going to run into is that if you can't do 75M damage to CB with the 4 keys you receive daily to complete this part of the questline then one of the missions following this one will just end up being your new "roadblock". 

For me (I just completed the Arbiter Quest last month) the most difficult stages of the questline were the Arena ones (time consuming as you need so many medals to unlock the Great Hall bonuses followed by needing 200 Arena wins) and the quest requiring you to complete the Stage 20 of each Dungeon 10 times on Auto.  

My advice would be to continue developing your Champions and gathering gear until you reach the point that you can do the 75M damage w/o buying extra keys.  

sinceramente ninguem  gasta em chaves, mas este  jogo tem muitas coisas suspeitas tipo toda vez que um cps sobe de lvl em campanha ou calabouços o dano dos npcs sobe como tambem seus criticos. chefe de clan a cada vez que voce entra ,muda tudo ja vi isso varias vezes nao existe estabilidade certa, eu desconfio que ha muita programaçao no jogo pra tirar qualquer vantagem . certa vez fazendo minotauro 15 subi maestria de 3 cps quando voltei ja nao conseguia mais vencer mesmo os cps estando mais forte. com certeza desconfio do seu dano ter baixado por causa das chaves que  voce comprou, no jogo tudo é um programa invista em outras coisas amigo tipo fragmentos pra ter cps melhores ,so uma das varias opçoes melhor que voce possa escolher. bom jogo

Like others mentioned, you should be focusing on your team that is normal for CB, instead of trying to rush that mission step. As a start, why don't you post us your roster here and we can try to help you with your team.

i

That's what I've got folks, thank you in advance for any advice.

Can we see the rest of you champs too? Since you have Rosh, there might be an epic or two in there where you could build a full Unkillable team.

That's my lot.

i

It's been a long time, admittedly, but I have a vague recollection of some team with Tower + Torturehelm as the stun/die target?

you need to do at least 10 mil per key then its easy

save 900 gems and you can buy for 100 gems 1 key