Pretty much, I used to like her for my Wind attribute since it lacked damage but lately she's just been useless, not even reliable for Ragnarok raids. Maybe her only use is to aid thunder Thunder on his quest to kill before you get killed, that's very conditional though
Yeah, technically with Mars you would be able to hit a "hypothetical" -65% Defense Debuff if you factor the numbers her pseudo debuff leaves (factoring Vine as well) which is utterly insane, was Hephaustus Raguel (A Frame ATK SR debuffer) or someone else? I can't quite find her on the Gacha...
And yeah I was running Joan with EX Black Propaganda on R4 Accessory Quests alongside Summer Sol, Amaterasu, Svarog and the R Girl with a -10% DEF Debuffer, I didn't even need the healing drops to succeed on a 100% success rate, Joan is pretty much my way to go with Fire but if there was something I was missing out on with those two Souls I had to know...
I'd say your observation is correct, sometimes I used neglect BP and go full A Frame to prioritize Ares' Nuke and attempt to get out of Rage as soon as possible, this is quite risky and tends to fail therefore I switched to a more "stable" strategy.
Since I got Dakki I haven't had any issue with the Raging phase due to her Double/Triple Rate up paired with Rampaging to the whole party, maybe this will be even better when I gather the Holy SP to unlock Shingen on an all out attack mentality rather than doing this with Joan, what has me worried is that this strategy won't work on the latter content (AKA Guild Quest Order) but it's still manageable with Joan and a Healer.
In my opinion another issue with Fire was the inability to use Mordred with an SSR Weapon since there hasn't been an Event with an SSR Fire Sword or Glaive, I don't run into that Issue since I have Gacha SSR Weapons for Mordred but that's a big hindering for Black Propaganda and Vicissitudes of Fortune to some extend. Disregarding that; since almost every Fire build heavily leans on Amaterasu Outrage ends up being an useless skill, that and all the Skills Joan disposes of are useful makes most Fire players ignore Mordred.
Speaking Ragnarok Advents they're a piece of cake for my Fire team disregarding the attribute of the Advent except Water but this quite changes if a debuff misses and you don't start with a loaded Sphinx, that's where Joan saves your butt, thanks to both who answered.