As far as the levelling method for Medic goes it does make some sense as medics did (and still do) learn on cadavers. I do however agree that XP gained is far too low. Maybe instead of increasing it have the skill gain XP from seeing enemies die as well? A dead body is a dead body after all.
It's possible that the initial behaviour was a bug but it's worth looking at how fixing it impacts the core gameplay loop.