Agreed - except, you will never be asked for your transcript for a postdoc. position. Your publications and interview seminar get you the position. The only exception would be if you decide to do a clinical fellowship (clinical biochemistry, medical micro. etc.), in which case, your grades earned in graduate school matter and you must provide a transcript for that position.
I wasn't asked my transcript for any Postdoc interviews. It was all based on my research track record, and presumably how influential my PI and other collaborators were and prestige of my program/school. Before I actually started the job I needed to send them a document that I actually defended and had completed all my requirements that I got from the registrar, but that was just for their records and to prove that I did actually hold a graduate degree.
One big difference between medical school is that you are told what to do do much of the time, or of your not told directly you can usually discover the expectations through a little trial and error or by following the example of other people, which is where some of the competitiveness comes in, as you need to be looking around and seeing what other people are doing. In a phd, depending on your adviser, you may only meet once a month to discuss what you are doing, and you have to entirely determine for yourself what you are doing and how you are going to do it. That can be extremely difficult.
Often that means that there is a much simpler reward cycle in medicine. You take a test, that's a high point and you get some feedback; you finish a rotation, you can take a vacation. If your working on a research three or four year research project, your basically wandering in the woods intellectually speaking much of the time, and that is very difficult.
As far as MD school being harder to get into, by and large that may be true for a bio undergrad applying to both programs at the same school. However, do many medical students think they could get into a PhD program at a top school in EE, physics, math or computer science? Good luck with that. Some can, but not many.
I have seen many MD students through fellows really struggling when they try to take one of these type of classes, ie an upper level stats or algorithms class.
In any event, in a PhD, you have to make an actual, somewhat substantial contribution to new knowledge in the world. That is harder than it sounds. It's not just your PI telling you to do a series of experiments. It can start out that way, but then the students need to morph into independent investigators before the end. It actually requires very different skills and abilities than doing well in classes and even just doing careful work in the lab. That's often where people founder.
Good luck, whereever your academic path takes you. Things will work out much better if you just assume everyone knows many useful, important, interesting things they can teach you, regardless of their degree. You will have much better interactions, and learn a lot more as you go along by being humble about your own abilities and knowledge. You can have wonderful interactions just finding out what little bits of knowledge and wisdom you can get from everyone you meet.
