Not my experience. I'm learning to sing, my spouse is a pro singer, she told me "pick a song, preferably one you don't know well so as not to be biased, sing it a thousand ways over and over, try it right, try it wrong, try whacky stuff, try nonsense stuff, talk it, rap it, twist it, warp it around, then do it all over again a thousand times, and finally, sing it your way."
Years ago, I was in a tiny town trying to teach kids to ride horses. It was a volunteer deal with a poorly-organized group. I was a fairly solid rider who had learned horsemanship through a patchy mish-mash of getting handed horses that were easy on beginners, getting handed horses who were way out of my league, buying an animal that was way out of my league (We finally match very well now after owning her for 13 years), and a few dozen lessons spread out over 10 years. I didn't know anything about how to teach children to ride. I honestly still don't know much about kids in general. Thankfully, learning and how to learn is super interesting to me, so I spent many a long drive home trying to figure out what components go into learning horsemanship.
Obviously these kids aren't going to go through my same experiences. They probably won't have a family friend who invites them out to ride a reliable, but energetic, old horse. They won't blunder into a job where they're spending 30 hours a week on horseback like I did. They've got an hour or so once a week to build their skillset. Teaching a kid the cues and posture and how to ride correctly - there's a thousand books for that. Getting them comfortable and to the point where they can handle a weird situation and a horse acting out, there's not much for that. I finally realized that while riding correctly and being held to a high standard by your instructor is very important, jacking around on horseback is important for making it second nature. (On well-broken, very well-behaved horses) try to whack the other riders in the arena with a lead rope. Play pony tag. Make dares, try stupid crap unless I tell you you're going to get yourself dead.
When you're always focused on what you're doing, you miss out on getting that instinctual reaction. I've come to call it fluency. If this happens, then _ . You've got to be able to roll with the punches and the best thing I've worked out for learning that is play.
Being free and egoless like a kid accelerates learning like that so well. Learning to ride as an adult means un-learning the fear we acquired along the way, which is often a big transformation for them, and learning things as an adult is hampered by the need to reconcile the new thing with what we already believe. It's a huge lift. I think mastery is achievable at any age, but the price is almost always "everything," because mastery is not technique, it really is a becoming.
While I was never pro, I still ride more days than not, and what I've arrived at from it is posture is the effect other people observe, but to your excellent point, only after we have polished a free and fearless foundation that comes from that time in the saddle, where everything just becomes natural. If we try to affect the posture without that foundation, we get heavy german seats and hands and floppy dressage legs. That affected rigid looking seat is about submitting the horse to our aids, whereas a seat that is the effect of the free foundation you can learn more easily as a kid is about releasing the horse's willingness from our need. The posture that is the polished effect of that freedom has more grace, like a dancer or a matador instead of that of a performer or a soldier. The lightness that is the result of it is the effect of a rider's patient posture, which to an observer, looks straight, but they can't see the underlying suppleness of it unless they are at that level themseves. If you ever see any old videos of Nuno Oliviera (the last riding master of the 20th century), I would say that his posture is an expression of this patience, which comes from his first hand knowledge of what is possible, and the horse is responding willingly because it is being met with the confidence of his knowing, and so when it moves, it is following him, but following at his leg, and really, through his body it is reading the intent of his mind. In this sense, the key to mastery is learning patience, and knowing when to be impatient.
Anyway, way to trigger a dressage bro, not a lot of opportunities for that on this site. :)
Six years ago I caught a cold that affected my throat. After four days, I recovered from every symptom except the phlegm in my throat, which has persisted continuously from then to now. It catches my voice and blocks me from singing normally. (And, unless I cough regularly, it builds up over time to the point that my airway can become severely restricted.)
This seems like it would be professionally relevant to a professional singer. Does your wife have any knowledge of such a problem, or how it might be addressed?
As an experiment, try eliminating dairy from your diet. While unrelated to your backstory / being sick, it's known among singers to avoid dairy before a performance to avoid excess phlegm.
I found one mildly locally active antibacterial throat pill that was the only thing that would remove some persistent phlegm like that. I'm not even sure if it was a cure, or just a remedy.