Since game requested it here is a loose comparison between Red Ginger and Kerria against the current Lvl 90 (18mil HP) Raid Boss.
Keep in Mind: My Kerria has Skill Level 5 and 4 Equipment slots with much better Equipment than Red Ginger. I didn't feed Kerria any ampules yet. So take everything written here with a grain of salt.
However overall i think even if Kerria didn't have the Skill and especially Equipment Slot Boni she still would have performed better than Red Ginger cause Kerria has dodge and her once unique Ability (More HP=More Damage).
We will test both girls in the same Debuff Team.
Red Ginger Variant:
Result:
Kerria Variant:
Result:
Kerria survived the boss and the battle ended after 9368046 damage. Red Ginger and the others fainted after 4 million damage.
I don't know if Red Ginger would have survived if she had 5 Skill Levels and 4 Equipment Slots.
Kerria's dodge and her once unique Ability (More HP=More Damage) are two of the reasons she is pretty much invincible. Sadly Red Ginger doesn't have access to those Abilities so i overall think A-Tier is fair for her.
Judge for yourself, guys