Im not sure if its this black an white, while everything your wrote is true and i do think that a more dominant role is way more fitting for Nika too there are some other things to consider aswell.I have big doubts about this. Being a full sub somehow does not fit at all with the personality of the MC, at least the way he is depicted throughout the entire first season.
He seems to enjoy "pulling the girls' nipples" and watching their reactions. Almost all conflict situations that happened to him were, to some degree, provoked by himself.
He either pushes people to manipulate them or asserts dominance, or help people he cares for (at least he thinks so)
He tells Nami that he is just as competitive as Zara, but most of the time he just doesn't care.
He tells Amber a lot about his assertive and aggressive side.
He acts dominant and aggressive quite often. When he encounters Vic's gentle and soft nature, he is almost afraid that he might hurt her and ghosts her for a while.
This is all totaly doesn't click with the complete sub role; he would rather fight with Vanessa and turn her into submission than submit to her.
Imo its evident that Nika likes girls who a) arent pushovers and b) are able to fight back, its not like he's only looking for submissive doormatts. Bella, Zara and Nami kinda prove this and the biggest indicator is probably Summer, she always fought back against him and he seemed to like it.
Domination and Submission in the Bedroom are in 95% of cases some case of temporary (Role)play anyway, i dont think Nika or any LI will end up in a weird real 24/7 sub position lmao