I don't think it's a restrictive story at all, especially because of the undercurrents in Mio's friend group. They all come from troubled homes, and stuck together because of shared traumas.People are assigning grief to Haruji based on how they might feel in that circumstance, but I don't think Haruji is most people. He did not and does not feel grief about Taiga's death. That I can say that with this much certainty because this manga is a made-up story and the ones involved in creating this manga specifically chose that narrative. Again, it makes for a bad and restrictive story, but it is how it is. Haruji is a bad, irredeemable person because he was written that way. I mean, no one said this was War and Peace.
I mean, you lay out a very convincing character of Haruji here. An entitled man who sees his wife as a sign of power and influence rather than a person, who's annoyed when she does things he doesn't want her to do and is especially annoyed that she forced him to be a father. Every action she takes that he doesn't want undercuts his authority and power, and that stings him. He's used to other people bending over backwards for him, and has gotten through life being pushy and forceful enough that people will. He's never really taken responsibility for anything, not even bothering to wear a condom, and even now sees Mio's grief as a slight against him.
Which is all bad. He's a bad person. But here's the thing, the other half of him? The other bad part? That's his depth. Haruji acts like a mob boss, or a landlord, or an evil CEO, but he's not. He's a blue collar worker of some kind that clearly makes decent enough money and who has a family who has some sort of generational wealth and influence. Fine. Good enough. But less than he's sure he deserves. What flows through every action he takes and every word he speaks is resentment at the world, at his situation, at the people around him who don't give him the respect he feels he is entitled to. You peg him as a narcissist, and I don't think you're all that wrong, but he's also a person we've all met, a particular type of shitty dude who feels victimized by his lack of power.
He is not one dimensional. He is, on one hand, physically powerful, demanding, has economic and social influence of some kind, especially in the town he lives, and is used to getting what he wants. But he is not content. He is resentful and insecure, convinced people don't respect him enough and that the reason they do things he doesn't like is because they want to slight him or embarrass him. Because in the end, he's not an impressive figure. He's an uneducated manual laborer who married out of high school and beats his wife. He's deeply pathetic, and he knows it. Which is why he's so angry, because he has to cast himself as the victim of an unfair world or his whole identity will collapse.
He's the kind of character that feels like a stereotype, like you said: the guy who peaked in high school. But I've met them. We've all met them. Entire political movements rest on the backs of these types of guys.