Isabel

• Isabel, on her own, it's trash. She only works because they introduced a buffer specifically made for her (Arcana).
• Low damage multipliers for Marked Target and marking system are only beneficial over long fights
• Reducing Full Burst duration for a majority of units is a downside and lowers DPS (this does not apply if using units like Arcana)

Not worth taking skills any higher, since all her damage is coming from Arcana buffs rather than her own kit.

Also not worth building if you don't have Arcana.