What preditor was so fast horses had to evolve to that extent??

Same for rabbits. The are basically as much lean muscle that can fit on the lighest possible skeleton.

If you pick up a rabbit wrong, they can snap their own back with the momentum from kicking their back legs.

Basically a 900LB Cocker Spaniel that's afraid of it's own farts and will eventually kill every single tree within reach. I also will never own horses.

To add on why broken legs are fatal: its because horses are so big, that even with a sling, they cannot support themselves well on 3 legs. And lying down is also not an option as their own weight will crush their internal organs if they stay down for too long.

From what i read here there's no unhealthy horse, it's either healthy or dead.

And they run around at 60mph on the tips of their toenails.

Humans have multiple toes because our ape ancestors used their toes like fingers. Having multiple, separate toes is probably bad for survival unless you're using toes to manipulate tools.

Animals that have distinct toes include apes, geckos, mice, raccoons and similar animals which need them to grip onto surfaces or to manipulate things. There are predators which have separate toes because they're a place to mount claws: eagles, cats, etc. There are animals that have separate toes with webbing between for swimming. But, for a lot of animals, separate toes aren't really useful, so they've evolved away: elephants, rhinos, giraffes, horses, cows, etc.