I was talking with Timo once, and I think we (or at least I) figured that the T'Kumbra wasn't all-Vulcan by design, but by expediency. Captain Jerkwad, probably newly promoted to command rank due to the pressures of war after being held back for years due to his overt and very un-Federation racism, was given a ship newly built/refitted at the Vulcan fleet yards, and, exploiting Starfleet Command's need for speed, he managed to fill the entire ship full of Vulcan conscripts. Of course, he set out to prove that Vulcans were the master race, in part by winning the war, but primarily by training his crew to become the finest baseball team in the quadrant (Cap. Jerkwad is not a well-balanced man and he does not have his priorities straight).
He was probably the subject of numerous complaints by his more conscientious subordinates after the incident in Take Me Out to Holosuite, and following the end of the Dominion War Cap. Jerkwad was likely either thrown out of the service for his frequent inappropriate behavior, or moved into a position where he couldn't hurt anyone. Maybe he was even ironically punished and assigned to some crap job on Earth.