Flat head screws had no problem with long screws in the 1800s when a human drove them in by hand. However with early automation in the 1930s there was an overtorque problem and so fasteners that couldn't handle the torque were developed.
Note that the blacksmith made screw drivers of the 1800s were hollow ground, or at least parallel. If you have a cheap modern flathead screwdriver it is probably tapered the wrong way and can't deliver enough torque. That is the fault of your screwdriver though, not the screw design.
Note that the blacksmith made screw drivers of the 1800s were hollow ground, or at least parallel. If you have a cheap modern flathead screwdriver it is probably tapered the wrong way and can't deliver enough torque. That is the fault of your screwdriver though, not the screw design.