“Xing wei is one of those Chinese culinary terms that has no English equivalent”

LOL! You’ve explained it quite adequately actually. “Fishy” in one word. Or more accurately, “fishiness gone rank’… at least when fish is involved. It also has the broader sense you indc=icate in relation to other meats but in my experience xing wei is most often used to describe fish that’s stale, or ‘gone’ or simply extremely fishy.