I had an MRI denied for a partial pectoral rupture. Which was a routine diagnostic as a precursor to open shoulder surgery to determine the extent and location of the rupture to figure out if surgery was absolutely necessary and to prep a viable surgical plan.

I had to fight the insurance company with the assistance of both my surgical and non-surgical sports medicine doctors.

The good news though appears to be that I imagined the entire thing, because denials for routine things never happen.

To give an example, about 60 to 80% of the time, when I visit the dentist for a regular cleaning the charge is denied and I have to submit additional paperwork to convince them to pay it. I can't think of any more simple and basic procedure than that.

I have no idea why your experience with healthcare in the US is so much better, but I can assure you that there are many people whose experience is more like mine.