Large animals that were difficult or costly to domesticate (like the Aurochs) were generally just wiped out.
My guess is if horses were carnivores they would be extinct or limited to a few in zoos and some of the wilder places (like tigers).

That one person you know who absolutely loves horses would be a lot creeper

The entire way their legs and hoofs are built. They’d have paws with massive claws and massive legs. They’d run more like a big cats.

Man I wish we had shittywatercolour here to draw this up.

Horses would probably be dead or endangered if they were more trouble than they were worth.

Carnivorous Ungulates did exist in the past

We would be riding cows instead.

Please send help. 🧠

I’m too busy imagining getting run down by a teeth-gnashing Clydesdale and pissing myself to answer the question