You don't even need Keepers Hymn. Stats are not shared between classes. Each class has it's own stat setup and point allotment. If you drop 50 stats into CNJ, you'll still have 50 to drop in MRD. Those points that you dropped into CNJ will only be on CNJ, then, when you switch to a new class, you'll have an entire new set of stats to allot.
In other words, you can have 1 character with every job/class without any downfall. In fact, it is recommended that you keep 1 character with every class so you have access to different skills.
The Keepers Hymn is mainly for higher level players that want to min/max their character to get the best out of their job for end game content.