But concept of opportunity cost means it's not just other Zn stocks it's where the universe of all opportunities intersects those attractive to residual holders of HRR.
I'll concede a (major) weakness of HC is that it tends to focus only on the benefits of individual stocks or their near neighbours not a portfolio. E.g. despite the current minor resources resurgence in the past two or three years one would have been a lot better off holding a portfolio of overseas stocks let alone the FANG's (US tech stocks- Facebook, Amazon, Netflix & Google ).