As a horse owner I do think equestrianism has lost it's way.
As domesticated species horses are very distant from their wild origins (in the same way dogs are very different from wolves). Just being out in a field is not enough exercise for many horses. In the wild they would travel for miles every day. So they need to be exercised, just as dogs do, and to build muscle in a way that carries a rider safely for both, because rightly or wrongly, that's what they've been bred to do (although some very badly).
So they're here and they need exercise. We can't just let them all loose to get naturally fit and they need to be supervised. Schooling or dressage is a way of training a horse to use it's body in the most effective way to build fitness as part of a varied exercise plan. A bit like going to the gym. The movements are all based on natural movements. If you haven't seen them, maybe you haven't seen a horse be turned out in a field for the first time in a new herd, or seen a stallion when he gets sight of a mare in season. It's beautiful to watch and a privelege to be a part of, when they achieve it with a rider onboard. Done well, it's a partnership.
Lots of people use "competitions" as a measure of how well they're doing the job and to get feedback on how they can improve from judges who supposedly are the best at it. But as with most things, we take it to extremes, especially when those that are doing well are then worth more money! We often push them to get quick results, and that's where we go wrong IMHO.
So it becomes about the competition and winning prizes and being the best, rather than about fitness and longevity of the horse. But I'd argue til the cows come home that there is a place for riding and dressage that's in the interest of the horse.