The numbers are not intended to reflect actuarial accuracy. They are intended to illustrate the fact that “costs” cannot be considered without looking at the (sometimes equally high) cost of the alternative. That concept is not irrelevant.
I agree with you, Seenie. The article, I think, is trying to underscore the fact that while the treatment of P and PsA are incredibly costly when looked at only in terms of the medications, there are also other hidden costs that are hard to quantify. And, as you suggest, if physicians ceased prescribing the medications the costs of the diseases would shift elsewhere.
I am having a particularly painful time of it right now because of the cold weather which seems to bring on a rather dramatic flare but I'm still mobile and able to work. I can't imagine how disabled I would be without the biologics on deck (and working). And even with the biologics there are the other meds I need, and physical therapy costs. But, yes, these are also still cheaper than the physical and fiscal toll of TJR.