Here is an example of what a character is fully quite capable (and is) capable of doing at lvl 20
Note that the (1d3 +1) is the 3 PP bonus damage slot towards X:
Basic Attack ~ 0 CP = (1d6 +1d3 +1) = Average of about 6.5 Damage and with crit (another 1d6) would be about 10 Damage
most people have this combined combined with:
Secondary Attack ~ 0 CP, 1 Round Cooldown = (1d4 + 1 + 1d3 +1 ) = 6.5 average and with crit about 9 Damage
This is to more or less reiterate Sleepy's point.
That's on average, about 19 damage dumped on one person for 0 CP. The average of a fully specced C-Rank Medical Ninjutsu (1d6 + 1d6)= Would be 7 damage at 4 CP. Of course you can factor in other such things such as slots but even the highest grade achievable at this point that only brings the CP cost to 3.
Overall, I would have to say damage is higher and intentionally made so because there is that chance to hit. As opposed to healing which always hits. Even if the hit rate for attacks is indeed 50%, a medical nin has to waste considerable amounts of resources to patch someone up after an attack. Not to mention the amount of resources he/she has to spend in order to attack or defend.
I would welcome any sort of counterargument of course since I only have so much information on me. (Considering I'm not even part of the staff).
Addendum: And solknight does have a point. One stun, and boom a person can be almost geek'd almost instantly. And healing would not even save a person a person at that point. (It would but one such power runs upwards to about 20 cp iirc.)