I made a mistake here. Visibility is not an actual mark of the Church. Forgive me.
Your error was only technical. While "visibility" is not one of the Four Marks of the Church, visibility is associated with one of them, unity, i.e., the "one" of "one, holy, catholic, and apostolic". The Church is a visible society on earth because it is made up of human beings.
The only difficulty here is when one associates the manifest heretic with that society. This would be like considering the prisoners in the prison and the townspeople of the town where the prison is located as being members of one society. Although both societies occasionally mix (the guards and other workers enter the prisons, sometimes prisoners escape) and it can be difficult to tell one from another (prisoners want to reform but remain in prison, some of the townsfolk should be in prison, but they have eluded detection and continue to exercise authority in the town as well as the gangsters who are well known for what they are but no will remove them from the town) and some members of one society claims to belong in the other (the prisoner who claims, "I was framed!"), they are still two entirely different societies.
In the same way the Church is a visible society in the world. The collection of Catholics make up that one, visible society. It is true that there are many in that society that are less than stellar. There are many who exercise authority but whose treachery has not yet been detected. And there are those who have openly declared war with the Church by proclaiming and defending heresies which put them out of the society of the Church even if most people are afraid of their prior positions in the Chruch and refuse to recognize the fact of his departure for fear of what others will think or the sanctions others will place upon them. Those conciliar officials who have removed themselves from Catholic society but continue to reign are akin to the gangsters in our example above.
I realize this is an imperfect analogy, but it can suffice for illustrative purposes.
You really were not far off.