Not just our dogs. People too. Look at the helpers who catch the dogs at 30+ mph. Tell me their backs or shoulders aren't out of whack.
I've worked dogs for decades. Now I am older, so get discounts at crappy restaurants but until recently, the only problem I experienced was sciatica. Was that from helper work? No, more genetic and I always have felt discomfort when just standing for long periods of time. The rest of my body was fine. Now I feel more age related issues but nothing terrible. I am still very active and still work dogs.
I attribute my ability to still do it, to the way I worked the dogs. When the dog would hit, my body would be relaxed so it could absorb the impact and I would not hurt the dog. I can't tell you how many people I have to tell to NOT brace themselves before the dog hits. It is a natural response and some helpers are doing it anyway.
Also, when a dog "hits back", something I encourage and I can feel the dog about to do, again, I relax so the dog not only feels powerful and can move me around, but my shoulders don't get ripped apart trying to prevent the dog from doing that. This is one thing I see helpers do constantly, they try to prevent it and it is not only bad for the dog, it is bad for them. The reason drunk drivers survive and the people who see the crash coming do not, is because the drunk is relaxed on impact.
I'm not talking about trial routine, there is a certain way the helpers have to work the dogs there, I am talking about training. We do much more of that as helpers than the latter.
How this applies to heeling, my theory anyway, is how relaxed the dog is while doing it. The method with the ball, asks the dog to exert more unnatural movement and seems more rigid. Speaking of chiropractors, I will say not all are created equal and I have heard some very bad advice from some of them, including avoiding x-rays, (to save money to give to them instead).
As for not liking the head up. You can certainly train the dog to heel looking straight ahead. People used to do it all the time. Just make sure he is paying attention to you is all.
Also, heeling should not be something you have to work and work at. It should come easier for the dog if you are a good trainer. It should not have to be worked on day in and day out. So, if you like the head up, you can do that and not cause damage. My dogs have lived full lives without any adjustments by a chiropractor. There are genetic issues with the back in GSDs and no chiropractor can prevent that from happening. Can they make it better for the dog? I would guess so but for me, maintaining the dogs fitness and his musculature is the most important. Stretching I think would be very useful.
What dogs do all by themselves didn't used to require this level of medical intervention.

Maybe the dogs were a little tougher? Or maybe the people were different. Some say we were simply animal abusers but that certainly was not something I saw over and over. People who were not in control of their emotions training dogs? Sure but who just sits in situations like that and says or does nothing? You either stop them or better yet, help them to work the dog a better way. I have found that to be the best way because most of that behavior is simply frustration fueled by not knowing how to train.
Anyway, relaxation is IMO a big part of this for both people and dogs.