I think CSS Alabama was a fine commerce raider against merchant ships. But it must be remembered that the first time she came up against an equally armed US frigate, she was sunk in an hour.
The difference, ultimately, was due to training and maintenance. The
Kearsarge's crew was well-drilled and cohesive, and she had had recent and regular maintenance and resupply; she was in much better condition at the time of the battle off Cherbourg. By Semmes' own account, the
Alabama was in poor condition and much overdue for a refit-- that was the principal reason she was in Cherbourg to begin with. I can't recall offhand which set of memoirs mentioned this-- Semmes', Kell's, or Sinclair's-- but a recent gunnery drill conducted by the
Alabama on her way to Cherbourg revealed that her powder had deteriorated and that her gun crews were a bit lacking in the marksmanship department.
On paper, the ships were about as evenly-matched as any two could be; the
Alabama was among the more heavily-armed of the Confederate cruisers and the
Kearsarge was one of the more lightly-armed Federal sloops. An interesting item giving further support to the maintenance conditions:
Kearsarge's speed trials showed her to be measurably slower than
Alabama, but at the time of the battle, their speeds appeared to be about even.
I highly recommend William Marvel's
The Alabama
and the Kearsarge
: The Sailor's Civil War, which tells the story of both ships and their crews, and is quite well-written to boot; I thought it would make a fine miniseries, actually.