As a general rule, the more material you remove from a flat pedal’s structure the better its self-cleaning properties are, enabling it to shed mud during a winter ride. A pedal structure with more metal removed also yields a lighter pedal, but you still need enough pedal surface to provide a sufficient distribution of pins.
Material and manufacturing improvements have enabled pedals that are larger, lighter and capable of accommodating more pins. Having pins around the edge of the pedal makes the most sense, because the axle body area, in the middle, isn’t where you source most grip when descending. The skills philosophy of ‘heel-down’ pedal technique applies force to the fore and aft, so this is where most of the rider input happens during technical riding.
Although we refer to them as flat pedals, most are in fact slightly concave. This rise at the front and rear of most flat pedals is a subtle design feature that isn’t as obvious as pin placement, but vital. This concave shaping gives you an intuition of where the limits of the pedal are when having to readjust shoe position during a descent.