[Zeitgeist]

engineers require more skill to fight off spies and defend effectively against demomen and soldiers. Medics cling to another character and follow it around. Combat medics require a lot of skill but are worthless in anything but games under 3v3 and arena.

learning how much curve your medigun can handle, at what distance and angle the tube breaks, is an acquired skill. as is body blocking, uber blocking, and generally good positioning.

medic is a lot more then just following another toon around, its following another toon around and NOT dieing.

edit: and as you mentioned, learning how to use the curve of the darts and the quick switch to ubersaw to pump the meter and add burst damage... learning how to position doing that against pumping health into another player... its harder then many think, and i think harder then just knowing good sentry placements to play engi.