I wouldn't tie it quite so firmly to certification level, although of course the rules do set the level of Medic-3 for a licensed MD. If you've been around medical personnel much, you realize that sometimes experienced paramedics or nurses know more about situations they encounter regularly than most MDs. Plus some doctors flake out and become burned out and careless, which I would reflect as a reduced level of Medic skill, regardless of the license held.
So we could see some Medic-3+ paramedics or nurses, and some MDs with less than Medic-3.
Mostly quibbling about edge cases I suppose, as in general I agree with your statement for the minimum Medic skill levels for certification.