As far as grinding through locks the quality/hardness of the steel has a major effect on the time required. The Kryptomite NY locks and Abus lock tested all apparently use high strength alloy steel, properly through hardened. Based on time taken in the tests the On-Guard lock apparently uses much poorer grade steel, probably surface hardened only.

I would be interested in seeing the Harbor Freight lock and trying a regular hacksaw blade on it. At that price I would expect the shackle to be nothing but low carbon mild steel. If so it cannot even be hardened except by surface hardening which itself is a relatively slow and expensive treatment.