Horses could be OP if tamable.
All it takes is one clover for me to destroy an entire swamp of fireflies and curiosities. The amount of ground I can cover with a single clover is also insane.
I love horses, and I think right now the horse implementation is about as fair and balanced as it can get. You can maybe find a couple horses in a big field, but if you could consistently gear up an entire war party with tamed horses - The average hermit would be in big trouble.