I think it has to be acknowledged that we're getting out of the arena of science and into the arena of merely empirical experience —which is something I do not sneer at, but something that deserves a name and a category of its own that the English language does not quite have a term for.
To give an example: if I met a man who said that he struggled to sustain an erection during sex, but then found that drinking hot sauce massively improved his sex life, I would not tell him that he was hallucinating (nor would I dismiss this as pseudo-science) but I also would not really regard it as evidence that hot chili peppers have a scientifically real effect on blood circulation --nor would I regard it as an indication that the subjective experience of eating spicy food is erotic/arousing as some kind of universal fact. If I met someone whose empirical experience was that drinking hot sauce really, directly, improved his sex life, I would treat that as an empirical reality, but I wouldn't generalize about it —I wouldn't try to construe it as something equivalent to a law of physics.
I have never, ever mentioned this on my youtube channel, for example, but when I switched from being vegetarian to being vegan, both my breathing improved and my eyesight improved, and this is most likely because my sinuses were slightly irritated by the low levels of dairy that had been in my diet before. I have no explanation for the change, but my ability to breathe clearly through my nose really improved when I switched to being vegan, but it is possible that the improvement actually did not have a cause-and-effect relationship with my diet at all --and, of course, the improvement in my eyesight is even more bizarre and inexplicable (and I have to wonder myself if it is more perception than reality, if you know what I mean: did something about my own psychology change, rather than my physiology, at that time?).
So, in this way, I think there's a category of empirical experience, of things that one knows, but never really knows with the certainty of a law of physics.
If you were on a 100% vegan diet for six months, would your aforementioned health conditions get better or worse?
I think the truth is: you don't know.
Many, many people report drastic improvements in joint pain when they switch to a vegan diet, and the primary reason for this is reduced inflammation, but there are probably complex secondary reasons as well (a vegan diet improves just about everything, including the circulation of blood throughout the body, so… there can be a lot of little improvements in things like joint pain without a single, simple cause-and-effect explanation). Of course, conversely, it could just be that some people who adopt the vegan diet are losing body fat and gaining muscle, and they attribute improvements in their joints to the diet, whereas its actually the result of weight-loss and overall improvement in health and strength —the list of conditions that are alleviated in mysterious ways with loss of body fat is very long indeed.
Will your joint pain get better or worse if you tried being on a vegan diet for six months?
The honest answer is: you don't know and I don't know.
It is possible your health would get worse in the specific ways you're worried about; but it is merely possible.
Now the following principle you will agree with: whatever makes broccoli healthy or unhealthy, good or bad, exists in the form of molecules within that broccoli.
We can put broccoli through a mass spectrometer analysis and figure out (atom by atom) what it is composed of: which vitamins, which minerals, etc.
If you ask me what it is that is healthy about broccoli, I can point to the molecules it is composed of. No more, no less: it is as healthy as the chemical components it is comprised of.
Have you ever examined, skeptically, what chicken bone broth is composed of, in this way?
What is the molecule, or what is the chemical, precisely, that you think is uniquely (or distinctively) healthy about this particular foodstuff?
Many, many people claim that chicken eggs have some tremendously life-affirming property, but this is more perception than reality, it is more psychology than physiology: atom by atom, there's really nothing healthy in eggs —and, on the contrary, they are remarkably unhealthy. This can be seen just by looking at their constituent parts, so to speak, atom by atom.
You seem to be confident that chicken broth is healthy for you, and even that it specifically benefits your joints.
Do you actually believe gelatin is good for your health? What is gelatin? It's an incomplete protein. Scientifically, why would it be healthier than (or have an effect different from) any other incomplete protein, or superior to a complete protein? I will state this as a scientific fact: any complete protein (vegan or non-vegan) will be nutritionally superior to an incomplete protein. Getting a complete protein from any vegan meal will be superior for the health of your whole body than an incomplete protein from gelatin in particular —and there is, chemically, nothing magical or special about gelatin.
Here is what wikipedia says about the matter, and I have not modified this in any way, aside from removing the links to the footnotes:
Some clinical studies report that the oral ingestion of hydrolyzed collagen decreases joint pain, those with the most severe symptoms showing the most benefit.
However, other clinical trials have yielded mixed results. In 2011, the European Food Safety Authority Panel on Dietetic Products, Nutrition and Allergies concluded that "a cause and effect relationship has not been established between the consumption of collagen hydrolysate and maintenance of joints". Four other studies reported benefit with no side effects; however, the studies were not extensive, and all recommended further controlled study. One study found that oral collagen only improved symptoms in a minority of patients and reported nausea as a side effect. Another study reported no improvement in disease activity in patients with rheumatoid arthritis. Another study found that collagen treatment may actually cause an exacerbation of rheumatoid arthritis symptoms.
There is no reason for Wikipedia to be the beginning or ending of anyone's research, but you must be aware: the link between gelatin and improved joint pain is dubious indeed —and reeks of what anthropologists would call "sympathetic magic".
In our culture, people believed (for centuries!) that the human body could not generate bones without eating the bones of other animals, and H.D. Thoreau refuted this by pointing out that the oxen on the farm were pulling your ploughshares with bones that they had generated from a diet of nothing but green grass.
I can repeat this with collagen. What is collagen, etc.?
And then for both gelatin and collagen, I must ask: is there evidence that the human body cannot produce these things for itself, without reliance on an external source?
My body, for example, can produce all the testosterone it needs without eating testosterone (and note: I say "eating", not "injecting"). There is no easy argument to be made that for our bodies to produce a given chemical we must eat precisely that chemical: the opposite attitude (that we must eat bones to produce bones, etc.) is just sympathetic magic.
The art of being an old man is knowing what you do not know, and working with (rather than against) your own ignorance, productively: to live with doubt as an oar, on the side of the canoe, rather than being ballast in the bottom of the boat.