Again-there are other disciplines that require an immense amount of knowledge, skill, training, whatever-dressage does not have a corner on that market. I hate to break it to you. There are knowledgeable, skilled riders in MANY other disciplines, so it is not "absent from ALL other disciplines" as you state. Geez.
Having to have an immense knowledge of DRESSAGE is absent from all other disciplines is what she meant. Might want to re-read some stuff.
I don't have to know about cows to ride dressage, same with people who work cattle don't need to know diddly about dressage to be good at working cows.
Also about the Clydy "winning dressage". Considering the bit in it's mouth is illegal at all levels of dressage, I'm highly skeptical. It looks like the rider is turned out for showing, not dressage, as well. Apparently our definitions of "doing exceptionally well" are different as well. Anything less than high 60% to low 70% at FEI PSG/I1/I2/GP I would consider to be marginal or average. A truly talented dressage horse in today's world is capable of an 80% at Grand Prix.
I will say this again. Good riding is the basis for all riding. Dressage is a sport. To all the dressage people whining about the sport being the end all be all of riding and how no one else can ride - you are the ones that make us all sound so snooty. A leg yield, a shoulder in, etc.. are not movements exclusive to dressage and should be included in any rider's repertoire as a basis to being a good rider. Being able to half halt a horse in such a way that they shift weight to their haunches while remaining in a connection, on the contact and swinging through the back in collection in order to increase suspension, impulsion and self carriage, however, is something exclusive to the sport of dressage. Dressage is not comfortable, it is not easy and it is certainly not the basis of all riding. Name to me another horse sport which wants the horse to be up in the contact having about 10lbs of weight in each rein, having the horse being so reactive that a flinch sends their hind legs flying and a shift in weight sends them almost completely sideways and wanting the horse to be on the absolute edge between control and freedom and expression of movement. Most pleasure riders want their horses to be easy to ride and that is the absolute antichrist of riding a good dressage test. One does not get 8s 9s and 10s for riding a subservient horse that is moving in a way which is easy to sit. I let a pleasure rider hop on my PSG horse and he was immediately flying sideways because the rider was not balanced in the saddle, that is dressage and it is the opposite of what a pleasure rider wants. A good upper level dressage horse is so sensitive that he dislikes being brushed, cannot be in certain blankets or handled by certain people and under saddle feels like a ticking bomb. Dressage is maintaining the sensitivity of the horse and increasing it to a point where they are balanced on the head of a pin. Pleasure riding is desensitizing the horse to the rider until it is "well behaved". The two are opposites and one is not the basis of the other.