It's a good idea, but instead of getting Gladiator Rank 1, I bet for unlocking new classes. Paladin Drk for Gladi for example.

Another idea is to be able to unlock these jobs at earlier levels, and leveling Gladi till 50 will grant you some bonuses for the unlocked jobs on that class. (More Shield MAstery for Pld, or more Attack power for Drk.)