Routine stuff is never denied in the US either. I've never had one thing denied ever and I even have a weird condition that requires expensive testing to diagnose and even more expensive treatment (narcolepsy). The insurance companies will throw up annoying bureaucracy like prior authorizations, and made me switch medication to generic when it came out (reasonable) and then back from the generic to another brand name when it came out (WTF??), but never actually a denial.
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.
Gemini states that an ultrasound is just as good for diagnosis as an MRI and is much cheaper. Could it be that the denial was correct and the mistake was from your doctor ordering a less cost effective diagnostic test, not from the insurance company?
And from my personal experience with narcolepsy, AI is a much better doctor than most human doctors.
Odd that your experience would be so different from mine. I routinely experience denials.
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.