I'm so confused about who you are speaking of. MC is Mok and ML Nanjo, right? Being the uke and seme is independent of them being a main character and main lead.
Mc is black hair, Ml is the white hair.
We read the story through Mok's POV, he's the main character, he's MC
Its the opposite, since everything is from mokyeon/ white hair pov which makes him the mc
Since he ls the top he is the ML I would say.
Those are not the same things, ML means "main lead", the love interest of the main character. Being the top/bottom is independent of that, but the confusing happens because 90% of the stories have the bottom as the MC.
Does the MC like the twink? I don't get ML, he is in love with MC and still went to this threesomes?