Ah, I'm going to point out that in that super-cute picture where your boy has TWO riders and a pair of batwings, and is obviously all mellow and groovy about it...
...what he does NOT have is a saddle.
So my money is going to go on "poor saddle fit" here. A good trainer can be helpful in assessing saddle fit, but believe me, it is no substitute for a professional saddle fitter. There's a saddle fitter that comes up to my area every spring, and sets up appointments at the different barns. My BO has been using the guy for years, he's very good. My saddle was the "best" fit for Huey and me and there wasn't anything *obviously* wrong with it when you looked at it, but it turns out that the padding over the stirrup bars was about a half-inch out of the position it needed to be in, and it was about a third of an inch too thick, and the padding in the back was about a half-inch too low. For $100 the guy did a full assessment of the fit (which was a VERY interesting thing to watch!) and then changed the flocking up. Even though it only took him about 15 minutes to make all of the changes once he knew what he wanted to do, afterwards, it felt like a different saddle, and my horse was moving MUCH easier under it than he had been.
So I learned there is a HUGE difference between a "good" saddle fit and an "OK" saddle fit.
I'm also going to stand up for good chiros. Mine told me it would be easier for *her* if I had the massage therapist come out and work on the horse before the chiro, but that it would be better for the *horse* if the massage happened after the chiro. And she doesn't make a big show of popping and cracking stuff, etc. What she does is actually pretty subtle and low-key, and the horse is OK with it, and he moves a lot easier afterward. He doesn't STAY moving a lot easier permanently, because he's 18 and the stuff she works on with him is the result of injuries he had years ago, and a decade of rough work as a professional jumper. If you catch stuff early, you can truly fix it in a lot of cases, but otherwise, you're basically managing it, not fixing it.