I guess it's because aerith can be a healer and time mage, which can make her very usable even in a non mono water team. S. Elsirelle is tankier and can do good deal of damage with unique strike magic attack, but she might struggle greatly againts magic tanks since she don't even have any kind of penetration and break skills. but yeah, I think they should be at the same tier at least.

S.Elsi and Aerith have different roles. It's a little early to really know where S.Elsi stands, so I advise everyone to wait and see her impact.

"A" for Tifa may have been too harsh since she excels at PvP. She's a solid unit, just less flexible in general. If it's a PvP tier list then she'd be S/SS for sure.

Whisper is S since she already has high base attack type resistances towards everything, which makes it easier to reach very high numbers if you have good gears. That and Quadra Break + Protection Break benefits everyone.

Whisper is not S tier I 🔥 her everytime easy

she can get over 100 magic resist, which nullifies magic attacks, while hitting 30 or more resist on every other resist aside from element, with no element weakness, and possibly 15 to 20 element resist for light/dark