Ok…sorry. Let me try…Why does someone that hasn’t ridden past those levels have anything germane to say about getting to grand prix? Because a horse is a horse is a horse.
We learn that 1+1=2 in what…Like when kids are 5-6 or 1st-2nd grade? And 1+1=2 is still applicable to a theoretical math PhD.
Same with the basics of horsemanship…someone like @eightpondfarm who has been able to train a feral horse to become a civilized equine citizen can have a lot to say about how a horse goes and whether it is well ridden. Underneath that GP schoolmaster is just a basic horse.
I took my husband, whose horses are the 4-wheeled mechanical type to Dressage at Devon. We were watching the warmup and he was pointing out horses that he thought were poorly ridden and cranked in. I agreed with most of his observations.