I see this sentiment a lot and don't really understand it. Until the last few books there is a very clear distinction between the human tech (hard SF) and the alien tech (magic). The main story takes place very much within the limits of plausible physics (ships rely on reaction engines and takes weeks to traverse large distances, space combat and weapons are actually realistic, powered armor doesn't keep people safe from inertia, etc.), and then there are magical elements that the characters run up against.
Contrast that with Three Body where the main plot driver revolves around FTL communication with indestructible intelligent nano-scale machines that can be anywhere any time, then gets progressively less realistic from there. I did enjoy the thread about the human ships going extra-solar, though, which was closer to Expanse in terms of Hard SF meeting a magical element (+dimensional travel).