Not so, actually - humans are one of the best at endurance walking out of all land animals. Trained humans regularly beat horses at long distance races - there's am annual one held in England, for example. I'd give links but I'm on mobile.
I think that's a major factor in endurance hunting - we can replenish hydration lost by sweat whereas others cannot.
> Although sweating is found in a wide variety of mammals, relatively few, such as humans and horses, produce large amounts of sweat in order to cool down.
We don't beat them out necessarily because we can replenish more, but because we are much more efficient at cooling ourselves. Obviously water and tools helped us, but imagine trying to compete in a 5k wearing a rubber suit--you wouldn't come close to competing with those humans you're up against.
http://www.cyclelove.net/2013/03/steve-jobs-on-why-computers...
I would like to know if these races allow for rehydration for both species, if humans run barefeet and if horses run with no cargo/horseshoes.