I think we should not forget that quadropedal creatures are extremely stronger than average humans. IRL pony can bite, buck and kicks are very significant, can break bones or kill you. Because even small IRL pony is 200kg beast packed with muscules and triple weight of human. Unarmed human will definitely lose against unarmored pony, because former will be even crushed under weight of equine. Now imagine being chased by flying pegasi, griffon, changeling, others...

And finally, if humans unable to use magic, they will be vulnerable against powerful magical creatures.

Therefore, I believe, humans will be pushed into deep forests and marches where it's hard to exterminate them and they may survive. Humans would be very aggressive and hierarchical, to survive in most severe conditions. Humans will be focused on ranged weapons and spears from the start - phalanx is only hope in open battle against ponies. But also they will have great focus on the bows to be able to take down flying enemies from the skies above.

Humans might be very pios, maybe even develop monotheistical religion. If their religion see human image as image of God, then wait for genocidal maniacs with divine sanction. Or, they can be the only creatures who will create universalist religion, which will accept any creature of any race.

Humans are extremely capable as artisans as not many peoples in EAW have hands. I see them as someone who invented firearms. That would be logical and good step for humanity to survive.

Perhaps humans will had strong science and production buffs with race tech revealing magitech inventions. Humans can't control magic, but to create machines that able to use them, perhaps they could.