Yes, that’s all kinda true. But that’s not the main reason for going to shows early. I’m obviously not a native speaker, so I’ll try to explain it in my own words. It might sound rude, but I’m not a rude person, just German 
I also didn’t mean to insult anybody and/or start an antsy argument…
In our opinion it’s never too early to get show experience, especially if you’re ambitious about the sport.
We think about the sport at the lower levels differently: in intro, training and even first level it’s mainly about the development of the rider, not the horse. Riders at that level are not supposed to and do not develop horses. Young horse classes are for developing horses, ridden by advanced riders. As far as low level riding goes, riding the horse “on the bit” correctly is a task that starts - hard to say in numbers - but I’d say 15-20% into your whole riding career. Before that, the rider is not supposed to mess with the bit before they’re not sitting correctly and balanced and before they’re not able to ride basic movements correctly in the arena. The aids required to ride a horse on the bit need to be developed over a long time frame, it takes most beginners several years. Why should they miss out on showing in that time (several years)? The focus is completely different in the lower levels.
Side reins are not supposed to tie the horse down and put it in a forced frame, they’re supposed to help the rider and especially THE HORSE. I know here in the US people think they’re a tool from the devil, but they’re not. They’re absolutely helpful and also healthy for the horse, of course if they’re being used correctly. Again, they help the horse to be over the back and have a steady contact without the rider interfering. Why do you use them for lunging and not just let the horse run around however they want to? Because they’re a great tool. There’s nothing wrong with that. They’re also not unsafe if used correctly. Riders who use side reins at shows typically also use them at home and the horses are used to them. USDF created the most beginner and especially kid unfriendly environment I’ve ever seen in my life, and we stand for something differently than that. We invite everybody to come and ride dressage, bring your jumping saddle if you don’t have a dressage saddle, we don’t care! But we want everybody to understand how important dressage is for every single equestrian discipline. Judges give you direct feedback on a microphone after your test, judges even help you through your test (at lower levels), that’s how it’s supposed to be! I took a 7yo to a USDF intro B test, she was the only one in the class and they disqualified her at her first show for having half chaps that weren’t smooth leather but had a little “fake leather pattern”. If that’s what you like then no problem, we don’t force anybody to come to our shows, we don’t even try to convince you. If y’all like it the way it is, that’s absolutely fine with us, don’t come please. But if you think that’s time for a different approach we’re open for everyone. We have a whole tier of dressage classes that are ridden in a group format and exclusively judged on the rider and the ride-ability of the horse. If you like that, come! If you don’t like it because you have a fancy warmblood and get 73% at USDF shows anyways, then don’t come. Or come anyways and give it a try. I just hope that everyone who doesn’t get tired of criticizing everything we do behind the computer actually comes to one of our shows to experience the atmosphere or at least talks to someone who has been there, I promise you’ll think differently about UDJC. That’s it, sorry for the long text and sorry for my English, I hope it’s understandable.
my observation for myself and others was that it took about a month of riding daily at all gaits before a new rider would “get their balance” as I called it and be able to stop grabbing mane or saddle horn.