I don't necessarily think calling hyesung mom is treating him like a woman .. it's more like someone who gave birth to him. They surely could've used dad/papa like it's used in our world, but this is omegaverse and since hyesung really got pregnant and delivered him, calling him mom doesn't seem repulsive or weird.
That's the thing I love the author but at the same time this omega verse where the omegas are essentially the submissive ones with no control I feel like it's so weird that they're using mom a female title to address him despite his pronouns being he/him. I think the author could have just stuck with papa or another derivative of dad because he's still a male.

I love love is an illusion and this but am I the only one who's weirded out he's called mom? Like I understand he's an omega and he gave birth, but I feel like it's so weird that they treat him like the a woman