In flight they shouldn't loose veterans( officers) cause SDE has turned that off, they do loose rookies and experts. Rookies are obviously worthless and experts you can rather easily regain, so the inflight reduction to crew losses a medic gives is essentially worthless.
As for the infrequent shelling, unless you're winning by the skin of your teeth you shouldn't get shelled as a CV. And if you're loosing you rarely get an opportunity to repair much. Combine that with a SD that's a lot of times not 900 SD and you'll get shelled a lot less than BB that can repair better and have 900 SD.
Given that veteran loss on a BB is already infequent, it's even less on a CV.
This makes the Medic a useless addition really.
Even a Seaman is a better crew member then. A repairman, an unused pilot, engineer for a free support/BO slot or gunners for AA/pHH are all better choices for a Medic as well.