Well, in this manga they’re established as humans with a mutated gene that gives them animal features (plus omegaverse stuff). So if they didn’t have human ears, The question begs: how mutated is the gene, and what are the variations? Plus, if it affects the visible features, what about inner body functions? (I.e without human ears the way they hear things and the way their head/ear anatomy would be different too. I imagine that would need to be explained, so it’d be easier to draw wth both anatomy, and say they’re human, but also have cat ears). At least that’s my understanding of it.
This is fun, and all that- and by the sound of it there's going to be fun consequences to that rut. But I really hate that habit of just drawing people with animal ears so they end up with 2 sets of ears. Think about it if it were eyes- and they had both animal and human eyes- ugh! Nope, one or the other, but not both.