Two problems with that plan:
- Black Propaganda buys you 1 extra turn without an Overdrive every 3 turns. Raphael's skill is on a 6-turn CD, so it's 1/2 as effective.
- Raphael's skill can be resisted. I've never seen Black Propaganda resisted.
Mordred is more or less required to do many Ragnaroks, assuming you don't have one of those perfect teams or unique kamihime that perform the same functions. For most players, she should be one of the first 3 legendary unlocks.
You can try with this setup, but you're going to be taking more damage and dealing with the debuff more often.