I think that's just the point of foundation horses is that its just a starter horse just to get ya going. Its not supposed to be nice 

the tradeoff with foundation horses is that they're always (except for limited breeds) available to purchase, and you can make as many as you want. customs are better than foundations and wilds are the best, with their tradeoff being they're harder to obtain.

The point is to breed better horses, so you get the Foundies and then try to improve upon them through playing the game.  Getting them leveled and skilled, pairing them to horses that will improve the conformation of the next generation, and so on.

If you want horses with better stats, you can absolutely get them from the Foundation Store, but they are less common.  I've had 5* 6 Excellent pulls before, but they're rare.  You're better off either buying from another player, trying your hand at capturing Wild Horses in Explore, or using Custom Tokens or Spectral Tokens to make a horse with better stats.