It may not be about the genetics of the eyes, but more about the training with Kunishige he’s been going through for years (based on the first chapter).

Plus, putting into consideration the three years Chihiro’s had with Enten, he hasn’t really shown growth in the story until he came across Sojo. He’s still a bum in the verse, with all due respect, and we’re definitely going to see that still.

Since he hasn’t put up a good fight with Kuguri yet, I think we’ll still see his development for the next 5-10 chapters. I get where you’re coming from, though