https://spendmenot.com/blog/medical-bankruptcy-statistics/
Medical bankruptcies represent 62% of all personal bankruptcies.
39% of those who have issues with medical bill payments already have employer insurance
I think you're right that if you have good insurance and you're wealthy you do ok, but it's easy to have employer medical insurance, have a serious illness, and have serious issues being able pay or expending a significant amount of personal wealth during that serious illness.