Here is the funny thing about things like this, normally to a cheater all that matters is their own personal truth. Also per my example I never stated I was the one that cheated. Also another factor is normally a cheater does not think what they are doing is cheating so they have a self justification that they use to validate their actions. You are trying to enforce a something they do not care about.
I said if I was part of a group and later found out someone cheated, and SE choose to take my clears away I would not be upset I would just shrug it off because I did clear the run and to me personally it was a legit cause I did not take part in the cheats myself. The OP could have easily just told the person to stop using cheats, and left it at that. The progress they made with them using the cheats would not be invalid or anything. Even if say they found out later the person cheated, and their run was now being questioned, if they had not know or the person lied and said they did stop but did not stop. I would personally just take the rewards away from the one that cheated. I do not think you should just blindly go and punish a group for the actions of one.
I do not get this stance you are imposing a standard they do not align with or follow, if they did they would not be cheating. Do you really think they care what the rules state? That is my point to them nothing anyone says or does will detract from what they have done in their own head most of the time. They will blame someone else, come up with a different story. People are having a debate over a topic that the party that has done the action does not care about in any shape or form. If you do not find it legit cool, if they find their run legit also cool. Why do people care so much if others cheat or not not like their was a massive prize pool and stake we are legit just talking about bragging rights and some minor 15 min of fame.
Overall I do wish people would take care of their own life and house before they start to question the actions of others. Overall that has always been my issue with this cheating topic, if someone does not agree with the rules and breaks them do you think telling them no you did not earn it would detract from what they did to themselves? Normally it does not, I have friends that brag about getting high ranks in FPS games but I am like bruh you use aimbot, they do not care. To them it still requires effort and still feels good. Banning them, shunning them does not take away the feeling they had in that moment. Same thing with my college mates that cheated on exams in school. They are happy as could be right now, they have good paying jobs and the past is the past. People will cheat and often a cheater will be okay with it no matter what one says or does to them.