Only non-retarded tierlist coming through.
Explanations:
Solo S tier: Are able to utterly trivialize the boss on their own.
Solo A tier: Can deal with the boss quickly and effectively, but still has to deal with basic game mechanics like dodging.
Solo B tier: Lacks damage or has their dps heavily limited by the difficulty of the boss focusing them or is vulnerable to RNG screwing up their spell list

Groups S tier: Contributes an absurd amount of damage and/or stance damage consistently.
Groups A tier: Needs RNG to line up well in order to delete the boss, doesn't bring more to the group than their own high personal damage or doesn't have high personal damage.

t. actually plays all characters