It's not really. The US medical system has this tendency to inflate pricing in a cat-and-mouse system where drug companies and insurance companies try to duke out what is the "correct" price of a drug. Setting it too high and the insurers won't cover it, too low and the pharmaceutical companies are "losing" profits to insurers. It's a terrible feedback loop that hampers those who can't afford insurance because the premiums are too high because pharmaceutical companies know that in most cases insurers will pay.
I think youre missing several inputs into your feedback loop. The original statement about the US system bearing the brunt of development stands. It's also true that insurers influence the market. Both are true. There are also government inputs into the market, political inputs a d supply chain elements that all feed into this. The one stakeholder will little real input in the end consumer who gets stuck paying whatever the others have decided they'll allow...
That doesn't explain the behavior of off-patent drugs being jacked up in price on a whim or near identical variants being made to extend patent protection and maintain the predatory pricing of the name brand. Their development costs are already recouped during the initial patent phase. Tweaking things a little doesn't cost them nearly as much.
