This is a very common misconception. It’s true, many Thoroughbreds have poor hooves.
But I would blame this not on genetics, but rather the fact that most are shod from a very young age (for racing) before the internal structures of the hoof have had a chance to fully develop.
Couple that with the stress of racing, and it’s no wonder many of them have feet with problems. But with the right diet, trim, and exercise, Thoroughbreds, like most any other horse, can go barefoot.