Yeah, the more I'm looking at this and playing and fighting her, the more it looks like I underestimated Djinn. I may go back and edit my initial review. It never even occurred to me to compare her attack stat to other diamonds, because Filia's don't have strong attack stats, but holy crap buckets, she's already one of the highest attack characters I have, and will probably be THE highest one I have soon, and that's before the permanent enrages like xcapibara said.
I've tried using her in a few 30-40 streak prize fights now and she's surprisingly effective even then. Debuffs and particularly bleeds are still king, but there's times when that's not an option, so she definitely has a good niche to fill there.
On defense, having fought a couple more high level Djinns, she's still a little random. Often not a problem, but has annoying moments. Having fought a max level Djinn on the boss node though, with the Great Escape catalyst to help her escape combos? It's a really a bad situation. I think I would prefer to fight Bioexorcist, if only because she's at least predictable and not randomly unflinching or invincible or immortal or reflecting my damage back in the middle of the highest stakes fight in the game.