How a slight change could open GLA for a future DPS job

[Reynhart]

The point here is: If we have a DPS job, Rampart and Sentinel won't be usable by that job since they'd be PLD skills. Rampart is not that useful for low-level, and by the time you learn Sentinel, you're already playing PLD and not GLA anymore.
GLA would still be a tank class, so Shield Oath would help it tank, but if you do a low-level as a DRK, you'd use Sword Oath instead of Shield Oath to be a viable DPS.
By giving less pure tanking skills to GLA, it would be easier to branch to another role, with the help of modifiers from a DRK crystal job.

The best part is that PLD wouldn't really change at lvl50 from what we have now, apart from a more powerful Sword Oath, with a slight drawback.