Well, I'm a veterinarian, not a physician, but the education level is the same, and veterinary medical school admission in the U.S. is actually more competitive than human medical school admission. Veterinary ER medicine is a specialty that requires a three-year residency even to be eligible to take boards.
I'm applying to paramedic school for this fall and have my interview in two weeks, but I'll keep working as a vet. So I can't speak for the paramedic curriculum yet, but I can say that the EMT-B anatomy and physiology was incredibly simple compared to the level we had to learn in veterinary school. We spent six weeks on the anatomy and physiology of the kidney alone.
Just an example. We learned in EMT class that there are "twelve cranial nerves", when there are actually twelve pair. That was all we needed to know. I believe in paramedic school we will have to know the names and general functions of each pair.
For my neurology class in vet school, which was an entire semester long, we had to learn the name of each pair; whether it was sensory, motor, or both; what areas were innervated by each pair; the route each pair took to the brain, including the names of all of the foramina through which they passed; and the area of the brain where the information was processed. We had to be able to look at sections of brain and identify all of the anatomical landmarks, and discuss in detail what each area or nucleus does.
That was ONE small part of ONE class during ONE semester. For three years we had full-time classroom, 15-20 credits per semester. It was like trying to drink from a firehose. I have about ten bookshelf feet of textbooks and twelve of notes. My dog and cat internal medicine textbook alone is 1400 pages long.
We were also taught how to "think like doctors". That meant we had to have a detailed understanding of the anatomy and physiology and biochemistry of every one of the body's systems, and be able to apply that knowledge to a clinical presentation of a patient who could be one of many species and who can't talk. To do that, we needed to understand biology, chemistry, organic chemistry, physics, genetics, biochemistry, etc., and we had to have that understanding going in to the very first day of class.
I could be wrong, and no doubt the paramedics here will correct me if I am, but I don't think paramedic school gives someone the background to enter that level of education. It's just a different way of looking at things. ER MDs are more than paramedics with more education--they have a whole underlying understanding of the human organism, based on their years of education, and they apply that to their cases.
It may not come into play during illnesses and injuries they see regularly, but when that big ol' zebra comes trotting down the hall, they have a whole base of knowledge and experience to draw on that they wouldn't have if they had gone directly from being paramedics to a limited ER MD-type training.
Having said all of that, I have a lot of respect for field medicine, and I love doing it. I volunteered at a Mississippi shelter after Katrina and just spent five days volunteering with 315 dogs who'd been seized from a "rescue". We had very few vets come to help, in a community where they are coming out of the woodwork, and several who showed up left almost immediately when they realized they'd be working in tents in a parking lot; with a lot of filthy, emaciated, barking dogs; tracking through mud; with no toys at all. They just couldn't handle working outside of their nice clean clinics.
I would imagine that some ER MDs would not handle field medicine very well either, outside of their comfort zone, without all of the fancy equipment and support staff. Crawling into a wrecked car and figuring out a way to strap the patient to a backboard might not be something they could do, but if EMS weren't there to get the patients to the hospital alive, the ER MDs wouldn't be able to do their thing.