Granted, I can see the point of "being a physician" being harder than "being a fighter". But I think that's because most of us, myself included, tend to underdefine "fighter".
I started a short, off the top of my head list above (diagnostics, 1st/2nd aid, biochemistry (pharmacology), surgery, etc., etc...). After some thought, it occurs to me that if you expected "a fighter" to be fairly well perfect EVERY TIME on tactics, logistics, grand strategy, psychology, games theory, leadership, etc, etc... in other words if you expected him to be to military matters as physicians are expected to be concerning healing....
....yeah, I could see it being about the same difficulty, and about the same time spent. The only difference between learning the two professions is who dies when the student gets it wrong.