I agree with your assessment 100 percent except for the 2-10% who are dissatisfied. I presently share email with fellow retirees from my former employer who have had TKR. the count is up to 14 now. We all have varies issues and different levels of discomfort but not one is 100% satisfied. Those that originally stated they were satisfied, when surveyed, admitted they had problems. Their original argument was "that at least the pain is less or gone," totally dismissing that now other issues like ROM and stiffness are present.
My personality is such that I have no hesitation asking patients in the Ortho waiting room for a show of hands whether they are satisfied. There were always some that were not. The term "crapshoot" is totally appropriate since not even the Orthopedic can predict the outcome.