There are tons of sorc and wizard that will out-weigh what you get from subbing them pretty much. Wizard and sorc subclass are also good in PvP but katar would be best sub for PvP because of that OP fast stun that procs before instant thunder anyway. Any main class that joins your party in the average run makes your subclass close to useless. But at least gunslingers are not that played as a class, also some subclass guns don't even use bombardment (or you could switch to Jaw Breaker if they do).