Well i could imagine it being decent if your teammates REALLY need the healing, but damage-wise there are better options for your money. SA80 is much cheaper than MedAR and does comparable damage while AK is still cheaper and does even more damage.
However unless you find yourself constantly healing teammates all the time, i usually find medpistol to be enough, since I'm usually killing things with SCAR and SA80/AK12. (Though I've been taking a katana instead of medpistol almost always now)
I agree with you. In my experience, if I am playing Commando or Support, and the team needs me to carry a Medic Rifle, it is because the Field Medic is dead. In that case there is a lovely Medic Rifle just sitting there for me.