Well, I recognized the elements you mentioned when I read the book, and yeah, there are elements of hard scifi in OBS, I’ll give you that. And going with the Wikipedia definition of hard scifi, it’s really a very arbitrary destinction between hard scifi and soft space opera:
There is a degree of flexibility in how far from “real science” a story can stray before it leaves the realm of hard SF. Some authors scrupulously avoid such implausibilities as faster-than-light travel, while others accept such notions (sometimes called “enabling devices,” since they allow the story to take place) but focus on realistically depicting the worlds that such a technology might make possible. In this view, a story’s scientific “hardness” is less a matter of the absolute accuracy of the science content than of the rigor and consistency with which the various ideas and possibilities are worked out.
It’s just that when I hear “hard scifi” I think of Clarke or “The Cold Equations.”