Well, it's rider on a horse. Would be fair if the human runner also carried another human on their shoulders.

Besides, ancient horses were much smaller and couldn't carry a rider, hence chariots. I would like to speculate that smaller means better thermoregulation, so smaller horses fared better on long distances versus Homo genus.

That's still a pretty short distances. I think in Ultramarathon, humans would win.

with carbohydrate gels, fancy shoes and years of training on the asphalt and a bunch of servants throwing you motivational words and ice water bottles?