Then let's hope that after she wins the custody, that she'll let him be her master without saying anything and it isn't just a consensual fantasy or game for her and start believing that Marc can also get physically dominating over her.
Obviously that isn't going to happen. There's a big difference between being dominant and being a bully. Why after throwing off the shackles of Anthony would Myriam allow Marc to behave in the same way? If you're expecting Marc to become a younger version of his father, and for Myriam to just accept it, then I think you're going to be very disappointed. Whatever sex games they play, Myriam is still going to be Marc's legal guardian until he turns 18. So effectively till then, he has to do what she says.
Also, to physically dominate Myriam Marc will have to bulk up considerably. He's about six inches shorter than her, and not exactly muscular. She on the other hand is being trained to fight by Lucy, who is a totally badass MMA fighter. Myriam only has to raise her voice to Marc, and he backs down instantly. Showing that his purported dominance is an illusion. To be able to physically dominate a person, you have to believe that you can do that. And Marc obviously doesn't.
Myriam is submissive, and she maybe needs a real man or a strong woman to dominate her. But Marc is not a man, he's an adolescent and a pretty immature one at that. It's not like Myriam is lacking potential dominant partners in her life. Charles, Danny and Nubia for instance are all infinitely more superior in the dominance stakes than Marc, and unlike Anthony and Marc, they would probably all treat Myriam with the respect she deserves. So if Myriam is going to eventually have a sub/ dom relationship, why would she choose the inferior option?