I have a question: if you don't want players to rush for it, then why did you set the limit at max level? That's sorta like telling a dog to take their time in fetching the ball: it either rushes for it as fast as it can or it just doesn't bother fetching it. Same rule applies to players leveling a job for a current CC skill: they either beeline it to the level of whatever that cross-class skill is, or they just pick up a job where they don't need that CC skill.

The only real drawback I see is that it'd be an absolutely massive systems overhaul for another CC system that doesn't really solve the problem of people feeling like they HAVE to level a class or job solely for CC skills (because it'll happen no matter how many times you say "you don't have to").