Breathing heavy after an extensive work out is normal... In the ring these horses give it their all, and exert themselves... They don't just piddle around the ring dragging their feet and going along lazily... They put forth effort and use their limbs.... That requires effort, and lots of it, the result is breathing heavy..... Breathing heavy is not abuse.... Nor is exersizing the horse to that point....
None of us have anything against working a healthy, fit, well conformed animal hard. Many of us are strong advocates for tougher conditioning of both horses and riders.
Explain endurance horses then.
Speed equitation horses.
Matadore or Picadore horses.
Eventers on cross country courses.
Far more effort. Far longer time competing. Far less lather and heaving.
Horses are capable of being conditioned and trained up to be able to handle these levels of physical activity in sport without any of the lather and heaving seen in a BL horse.