On top of all the awesome suggestions in this thread... some basics need to be covered/changed.
1. Swapping oaths (for us and drk)
Why does it take a gcd? Why does it cost MP? Warrior loses nothing from defiance >>> deliverance. Ninja nothing from wasp >> viper. Healers nothing from nothing >> cleric stance. However, PLD/DRK lose mp? To switch in/out of dps? It wouldn't even be a balancing issue it would simply make the job less clunky and more mp efficient.
2. Clemency interruption and scaling on spell speed...
Why is this even an issue? This is our only good heal, why can it be interrupted? Is it because SE doesn't know how to code a spell that cannot be interrupted? IF that's an issue have us build stacks in oaths that can let us instantly use clemency.
3. TP issues
Modify some skills to help us recover tp, maybe spirits within, since royal authority helps us recover mp already. (Then boost the amount of mp RA gives us)
4. Threat
RA needs to give a massive threat boost. Butchers is technically "strongest warrior combo hit" and gives them enmity bonus. This should apply to RA.
5. Tempered will
Make it do something else in addition to it's current ability.
6. Shelltron
I've sat and thought... but no it's just bad. Make it a mini rampart but slightly better. 45 seconds CD, 10% flat damage reduction.
8. AoE
Make flash perform differently depending on the oath your in. So you can have it do AoE damage w/ high threat in sword oath but in shield oath it just blinds? Something along those lines... or perhaps the reverse.