So I managed to beat Rahab Ragnarok. This time all my stat debuffs stuck. Things were going peachy, but then I think (?) I forgot to remove one of the attack buffs (buff/debuff meter was full), and the Rage Overdrive killed 4/5 of my frontliners except my Soul. Still managed to squeak out a victory since my Full Burst had reduced most of the Rage meter. Basically, if my affliction resistance down lands, I'm good. Otherwise, I'm fucked. Yay for poor gameplay design.
In any case, my experience was a fluke of sorts. You don't want to eat a Rage Overdrive with an attack buff up. For most players, that means ending Rage before her fourth Overdrive on turn 11, or bringing two sources of Dispel (i.e., Sol + Chaos Magic). If you push her into Rage before turn 6, then you only have 8 turns. Joan to mitigate the damage might also be an option, and that would buy you 2 more turns.
Water teams should consider bringing Belphegor, as her Rage reduction almost guarantee that your Full Burst will end Rage. Her stun extension will likewise make the rest of the fight much easier, while her type B debuff provides much needed redundance. Don't let affliction resistance down wear off or you might not be able to reapply debuffs.
I also beat Medusa, but it was much closer this time. I got lucky with Petrifies again, especially at the end. I felt like my damage wasn't quite what it should've been, which drew out the fight. I tried Jorm as primary eidolon this time, but I'm not sure the +20% HP is worth the -8% damage in this case. More HP means less Burst generation from damage dealt, and a partial 2nd Burst is necessary to end the fight quickly.