There is a man vs horse marathon since 1980, 35 kms/22 miles on rough terrain. There were 42 races, 4 times a human won: https://en.wikipedia.org/wiki/Man_versus_Horse_Marathon
Yes, but:
Horses are ridden by humans so the horses have to carry not only extra weight of the human, but also the saddle, gear, human’s water, etc.
Horses are mandated to stop periodically and mandated to have periodic stopped vet checks (rules now state that vet stoppage times are subtracted from Horse times)
Humans are NOT mandated to stop periodically and/or have health checks
There are places allowed for humans to have refreshments along the race.
https://afan.ottenheimer.com/articles/myth_of_persistent_hunting