Marc is a little goblin, while Catherine is a +1.80 meters tall and fit woman who started doing gym and martial arts after finally having the courage and willpower to kick her shitty husband out. She is the one setting the boundaries on their relationship either in a dom route or a sub route with shitty junior. He has no balls to challenge her if she talks serious.
Physical and psychological are not the same, the reaction to one situation does not mean a complete change, and the interactions with (and attitude towards) one person is not the one towards another, although of course that has also to do with the choices the player did all around, not only directly with Marc.
If one played in a certain way, Myriam reacted to the perceived threat to Katherine, under the push of her strong mothernal instict, and in reality, if she
kicked Anthony out (well, for the ones that play with the incest patch thus the original family relations, otherwise, he is still kicked out in the end, but not as husband) only after the secretary appeared home, it can be considered that her reaction was also linked at least in part to her mothernal instinct, the secretary being a bit like seeing her daughter.
The principle of submissives being actually in some sort of control of the boundaries (e.g. safe word) is valid in a context of erotic play, in the context of a form of abusive relation, even if not as pushed as the one with Anthony, the situation is more "tricky".
Effectively, Myriam reacted to the reference to Katherine, but otherwise,
with Marc either she was dom, or she avoided completely, or there was no "safe word" kind of situation, Marc even pushing in some situations without negative consequences, despite her trying to say no.
Not to be forgotten also that, again, depending on the way the player played and made Myriam think, act and react, Marc has played in part also exactly on the mothernal protective spirit and some sense of guilt and self-doubt.
I would agree with the last phrase, but whether she does that, does not depend only on the fact she is taller than Marc and has kicked out in a way or another Anthony, e.g.
think about how she could be if she get submissive all the time with all her other sexual partners .
It depends on more than one factor, it is part of the appeal of the game, it does allow the player to decide in part how Myriam changes, and thus how her interactions and reactions change.