In the databook she has 29, 5 points. This means she is easily a mid level jounin. And considering the fact she is the head of the medical team, means she is a good medical ninja. But I'm sure Sakura will surpass her. Apparently her chakra control is better, 'cause she was able to master the Chakra Enchanted Strength.
I am aware of it, but when you rank someone you need more to work than just someone else saying person X is really strong/skilled/smart and to take their word for it with no feats to back it up. We just never got a deep insight on Shizune's medical carreer outside of being Tsunade's best student until Sakura appeared, we were never told about famous notable surgeries she had or how many students Tsunade ever had for that matter. We just have Tsunade's word in Part I and even that becomes debatable in Part II once Sakura becomes an outstanding healer and shows it, as far as I am concerned Sakura may have already surpassed Shizune as she already has shown a better chakra control than her.
Shizune may be a captain, but so is Ao and he never showed us something to make him stand out from the other sensors. Did you already considered the possibility the reason Shizune was nominated captain may have been because she is Sakura's senior, traveled the world with a Sannin and as a result may have seen more from the world than Sakura? Those are good reasons to make someone captain in a war, but not necessarily means she is superior than Sakura in medic knowledge and prowess, maybe she just commands better.
By the way I took into account her medic screentime. I didn't forget about the surgery she made on Neji in Part I and I admit that was impressive, but Chiyo has a jutsu that saved Sakura's life from Sasori's poison as well and can bring people back from the dead and that's why I put her there. I never meant 7th place to be something bad, she has the 7th best medicinal prowess in the whole world in my book. That seriously looks bad for you?