The 79XX series of hooks were forged hooks (casting). Which means that the hooks are brittle and will break.

Wire hooks are rolled to align all the metal cells so that the hook will bend, which means they are not as brittle as the forged hooks. The molten metal is extruded as circular tube and stretched through a long line of rollers that reduce the wires diameter to the finished wire diameter.

If a wire strand is allowed to cool slowly at air temperture, the metal is soft (annealed) to strengthen the wire you heat the wire until its internal material is super hot, then quick quench it is a liquid brim to rapidly drop the internal temperture. That is referred to as Heat Treatment.

Most dry fly hooks are wire constructed not forged. The wire in the the hook will bend instead of breaking when too much force is applied to the hook.

Cast Iron is brittle, and will tolerate large forces on it in compression (your fly tying vise head). If you exceed the maximum pressure, the object will crack.

While wire will be able to bend (as long as you do not pass it point of elasticity) and will return to its original shape. Otherwise the wire suffers internal damage with ruptures that will soften the metal (steel) or harden the metal (copper).