I'm sorry, but I think people may be getting the wrong impression in what you are saying. Not you're fault out all, just people are probably misinterpreting what you are saying.
To clarify, flight surgeons fly in airframes, they ARE NOT the pilots. They ARE (for lack of a better term) "back enders". While they may fly in fighter planes, they are usually either a) Too busy seeing Sick Call, Annual physicals, Shop Visits, Whining/Hypochondriac dependents, Meetings (usually unrelated to our practice) or b) there is no room for them to fly. In addition, I found with most of my friends that are flight surgeons with fighter squadrons are having a hard time meeting their 4 hours/month flight requirement.
If you want to be a PILOT, you have to go to UPT (Undergraduate Pilot Training) but first you have to be released from your medical responsibilities (A hard task in and of itself). Not sure whether or not you have to go back to O-1 or not.
As for being an astronaut, we had a O-6 AF flight surgeon you was an "Astronaut" come in and give us a lecture at AMP. He had never gone in space and was instead doing all the physicals/sick call for NASA. I have heard stories of flight docs going into space, but I don't know who has done this and what requirements he had to complete. If you want to do this, they usually take the RAMs (Residents in Aerospace Medicine). The usual/frequent progression is FP/IM residency, 2 years minimum in that specialty, switch to Flight Medicine for 2-4 years, train in Aerospace Medicine (Combined with Occ Med/Public Health), enter into a Command position (i.e. Chief of Flight Med) with usual progression, then apply through NASA (as active duty or reserve). Other docs have done it different ways, but this seems to be the most direct approach. It goes without saying that this is HIGHLY competitive
...So to summarize, Med School IS NOT the "back door" into being a PILOT
