IMO, if you're not using paralysis and thus have to actually worry about the fight, bring a dispel (Chaos Magic in ex slot as an example) or use Cassiopeia directly. At a lower power level, you can get a lot of mileage out of her with the union buff that boost heals.
My thinking tends to be that if you expect the fight to be shorter (single digit turns), you go more offensive to try to speed things up further. When you expect the fight to take you longer, then you actually need to plan around that and focus on stretching out your survivability. It can be via more healing, or damage cuts (Joan), or Mordred's combination of Black Propaganda and trying to dazzle/charm with Outrage.

If you are going for longer fights, IIRC, you tend to prefer eating the raging overdrive instead of the normal for ult since you're more likely to prefer damage to be spread out over everybody instead of focused on a few due to # of party heals versus # of single target heals. And for expert, it's flipped around since for that one, it's the normal overdrive that hits all and the raging overdrive that hits a single target.