Tall and short people each have advamtages, but an ability to move with a horse who moves a lot clearly goes to the taller riders. Ideally the rider and horse have the same length legs - athe 5’1", my 16.3 guy’s legs reach up to my rib cage. Because I’m short waisted, my ribs actually overlap with the top of my pelvis if I don’t actively use my core topographic lift. But 9n the plus side, I never get the wiggly midsection taller riders can, and my legs are totally still even when relaxed and not gripping at all. That bouncy foot look so many have is a flaw I’m almost incapable of doing.
I think (hope) that part about not realizing top riders had to work was a joke. But yes, it can be a shock to ride big gaits the first time. A soft back is not hard to sit as far as the mechanics of how it works regardless of the size of gaits, but larger gaits certainly take more core strength for your own self carriage to stay either the greater amount of movement. It’s like trying to stay sitting as if the road is smooth on bumps at the front of a schoolbus vs the back. I rode my trainer’so mare with international quality movement about 6 months ago and couldn’t manage to even ride her canter much less sit her trot. She was tight in the back and sucked back at the time. I just had a lesson on her Friday, and discovered her gaits are now easier to sit than my TB’s, but they take more core strength. She is now swinging and more relaxed, though very clear about the balance her rider must have or she will passage or drop out of the canter.
That said, a rider needs to learn what works for them. I do better on the larger movers who have the long, range strides and you have to build suspension than I do on the large movers who float like my trainer’s mare. And my mare I show has super rideable gaits and over time is developing larger gaits but it’s not innately there. I intentionally bought a smaller size and less dramatic gaits for myself, and through working on riding her properly will be ready for larger gaits on my next hypothetical young horse.