It is not being short that gives the advantage it is weighing less. That means less work to move the body. However, given a certain weight long legs will provide an advantage. For instance Hicham el Guerrou, the current world record holder in the mile has the same inseam as Micheal Phelps who is seven inches taller.
For any objects, weight scales with the cube of height, assume the two objects have the same proportions. And strength scales with the square of height. That’s why, for example, ants are so proportionally strong. It’s not anything special about magic ant muscles, it’s just that they’re small, so their strength is proportionally much greater than a larger animal. If a human were scaled to the size of an ant, it would be much stronger than the ant, since we have evolved (proportionally) much larger muscles to handle our (proportionally) much greater weight. An ant the size of a human (say, 200 times longer) wouldn’t have the strength to move at all, since the muscles in those spindly limbs would only be 40,000 times stronger, but it would weigh 8,000,000 times as much.
“ideal” running physiques change a lot depending on the distances involved.
I heard Michael Johnson talking on the BBC about his own body shape during the recent world championships. Short legs long body - the latter giving stability whilst running (apparently). Short legs for quick stride
For long distance, as noted above, light is good.
and then there’s Bolt - the skill is having the muscle and balance to get into his stride so quickly for a tall man. Intererting article around the subject below.
Finally, I understand your username!
EDIT: And so, apparently, did others!
Tall people, in general, will have longer legs, & therefore a longer stride.
Short people, in general, will have shorter legs, & therefore a shorter stride, which can equate to more steps per time period.
First, the above are generalities, not necessarily applying to any given person.
Second, either extreme (few, long strides, or many, short ones) is probably not the most efficient but probably somewhere in the middle - above average stride length coupled with above average leg turnover.
Finally, there are many other factors involved, how in shape one is, % of slow-twitch vs. fast-twitch muscles & race length - 100m vs. marathon, aerobic capacity, etc.
It would be interesting to compare average height of best runners with average height within subgroups, to better control for genetic and cultural variations.
Almost all the best marathoners are from one small subregion in Kenya. So it seems unsurprising that the average height of the best runners might match median height of Kenyans.