Does the size and shape of the pedal matter?
To a degree, yes, because it impacts the amount of surface area you have to lay your power into when you pedal.
When it comes to the best pedals for road bikes, each brand makes claims about its system offering the biggest pedalling platform or surface area. It is an essential factor to take into account, as a pedal with a larger surface area will distribute your pedalling force over a bigger section of your foot. This might mean that five hours into your all-day epic, you might not get those uncomfortable hot spots in your feet, although the best cycling shoes will have stiff soles to help distribute pressure more evenly and increase pedalling efficiency.
Ekoi has taken this to extremes with a pedal system which broke cover in early 2024, with an enormous but skeletal pedal body, presumably paired with an equally enormous cleat or some alternative shoe connection.