I agree with you Warrior.
However minor the piriformis may be compared to the gluteals, their in-ability to stabilize the hip cuff and control the femur (both in dynamic movements & in stabilizing movements) is paramount. IMO- the hips cannot be looked at from a spot training standpoint but in totality. So the psoas, piriformis, spinal erectors & abdominals all play a equally vital role in the athlete’s performance & therefore must be trained together.