I think it depends how you look at this light novel. But for starters, it's an 18+ light novel focusing on adult material. So, in a way, being porn oriented is expected. Within the 18 chapters that I read, it sums up as a lot of sex related scenes, apocalypse outbreak, food scavenging, base building, zombie clearing, and family searching. And everything but the sex related scenes adds up to maybe 3-4 chapters.
In a sense, it's a really slow novel with a lot of fillers, but in this case, it's porno fillers. Really dunno where the novel will go as the protagonist is still a good guy.
There's a similar light novel with less sex related scenes (not saying none but less). It's called Only I am not attacked in a zombie world, or something. Protagonist can't control zombies but zombies will ignore him. So, he does necrophilia as well. But he's a total selfish ass, who blackmailed a girl to sex. And thinks of using kids as manual labour. Not a good guy protagonist but a lot more plot, so for those who dislike the porno fillers, go try that one.