The whole class system was set to reward you for learning skills from other classes, yet keeping some of them restricted to a class. However, the job system is rewarding for its extra skills - however restricts skills from other classes and gear in exchange.
I think Classes these days are about solo adventuring - you'll be able to do everything for yourself from the overlapping class abilities.
A black mage can use second wind and necrogenesis to heal themselves, however only as thm would they be able to do both of these and also use cures and protect/stoneskin (and raise).
The Job system should be about playing as you're needed - a block to fit every hole.