G'day Mac.
The other view is that because there are less decisions made in short race, they become more critical - make the wrong choice & you're gone. In a longer race perhaps a wrong decision can be countered by making a few better choices later in the race. Who knows?
It could be interesting to study the results of both types of races - if you're right the 'top jockeys' should do better in longer races, while the short races should be shared around a lot more.

Bomber