I prefer that they respect those who wish to use Blue Mage as their main class in the game by setting requirements to meet, with the understanding that Blue Mage requires a lot of extra work put in to reach a certain amount of skills (maybe all) to be usable at 70/80 alongside other jobs. Create many skills to be integral for use in winning Masked Carnival bouts, but make a system using a basic loadout of skills that can be usable alongside other classes in a typical instanced fight. Once Blue Mage learns a number of these skills by certain levels they are allowed to queue with other players.

This puts an extra burden on players that wish to play Blue Mage as a normal job, but trust that players will enjoy keeping up on skill acquisition with the hope they may rejoin content and also enjoy having further abilities to work towards in their free time that may be used outside of duties.