I actually couldn’t care less what a rider looks like in a class where the horse is judged. I prefer functional form for the rider, it’s actually more pleasing to the eye, but if the horse is balanced and moving properly, I don’t care what the rider’s doing.
I DO care when horses aren’t moving functionally well, which is what a lot of HUS and WP horses are doing. And yes, every other discipline there are either individuals who move incorrectly and are appropriately docked for it, or the discipline as a whole moves incorrectly and it’s the “best of the worst” who wins.
The rider is irrelevant unless their position is the direct cause of that dysfunctional movement. Polls below withers, necks broken at C3, not tracking at least into the front footprint, no moment of suspension at the trot or canter, not functionally correct movement.
When a rider is putting their hands around their knees in an effort to guide the horse’s head so the poll is below the withers, that’s a problem. IMHO, a lot of non-functional riding in that area has been created in order to facilitate some movement that is far removed from functional
That doesn’t mean that riders can’t have terrible form AND a functionally correct horse. There are a lot of Jumper riders for example who are just so WEIRD in their over-fences position, yet the horse’s still do their job correctly. And face it, a Jumper rider’s goal is to get the horse around in the time allowed, without time or obstacle faults, not have textbook perfect jumping form.
But they can get away with it because their foundation is almost always in correct, functional equitation, and they’ve learned to control their bodies so their incorrect position doesn’t interfere (much). Some of the winningest Hunter riders at the top levels have terrible form, yet manage to produce round after round of perfect takeoffs, knees to eyeballs with a round back jump, time and time again. The horses are going around so well despite the rider flinging himself on their neck in a (sketchy) effort to convince the judge that the horse is so round and powerful.
A lot of riders can get away with less than great position because of hours and hours in the saddle. And, some of those realize that by fixing a few things here and there to be more functionally correct (ie hand and arm positioning), they can get the same or BETTER movement out of the horse, with less work on their part.
Form = function. Always has, always will. There’s a reason for it.
The post is about thumb (really hand) position and what is correct. And when it comes to the rider, correct should ALWAYS be about what is functionally correct. The OP said thumbs angled in a bit is more comfortable, and there’s a reason for it - it creates the least amount of effort and therefore tension between elbow and fingers.