Only if you happen to lack money. If you have enough money, lots of diagnostics is performed, often helpful and insightful. I sometimes watch a TV show where people with rare and difficult illnesses are presented. One thing that was conspicuous was the amount of imaging, laboratory and other diagnostics that was performed, often repeated over and over again, furthermore senior physician treatment. In Germany, only persons with a private health insurance get such things. All the others...can watch and die. I read about two cases of MCAS (in the US). The thing that hit me was the fact that all kind of tests were performed, that the doctors searched long, and that at no point psychological diagnoses were a topic. I can imagine that private doctors can't afford to give psychological diagnoses too often, or else the paying clients might run away. So what might be universal is the fact that rich people get a good treatment with higher probability. Apart from that, my impression is that the US have better technology.