Justina works quite well against non-mystic units, but not as a damage dealer. In this case she's a kind of debuffer. For example, Justina's Penitent shot is one of the few attacks Samiel would dodge even in undying state. ^^ Against Konosuke, too, it's a good maneuver. Or against Odin...
But, the main advantage of Justina is the perfect synergy she has with any saint that could be on the field.
Luzbell : like for any inquisitor, Justina can be thrown into the enemy group at any moment. Yes, it prevents from really annoying combinations, like Aoi giving Coral extasy to Konosuke at the very beginning of the turn, or Reindhold paralysing you too early.
Evangeline : turns Justina into a incredible tank with 11 defense and 4 armor. On the side note, that's 90% of the time better stats than 8 defense and 7 armor. Then just add Blood omen (with Suppression aura to trigger it) or Raphael gift and she becomes near impossible to kill. Healing, Unshakable faith, etc. are just nice bonus.
Zack : A 5/10 attack with 2 dices and critical mastery ? Are we playing Empire ? Seriously, the dices manipulation power of Church makes this a pure execution on most mystic units... And so on. Elienai, Astraega and even Khaine or the church agent are also very funny with her. (Penitent shot + Hand of god = cry, baby
Only her ability to Blind enemies is really near to useless. Most of the time, you'll find something better to do with 2 ap.
Damien & Justina are scaring because the two of them makes a group that can be a pain for any organisation.
- Damien counters the processus and the gears, Justina only breaks metal.
- Damien turns Konosuke, Ophiel and any Coralextasied unit into dust, while Justina is a huge threat to 2/3 of Samael.
- Damien just * empire up, while Justina can seal really annoying units like Samiel or Odin. The pair MacBeth & Lilian is also over-used theses times.
- Damien counters arbiters and Justina "key" units like Adolf/Arkaid/Reindhold.
Althougt I'm probably not objective, I think both of them are really good 45 level characters.
Edit : Owned by two messages, how slow am I. ><