Moiraine is probably 2x a Sister like Kairen or Temaile, "middling " while Cadsuane is probably 2x a Sister like Tarna or Masuri.

Realistically I think Cadsuane is probably closer to Egwene than Moiraine as her quote is much more specific regarding strength than anything Moiraine says, and Moiraine is also clearly rationalizing when she's speaking of how much stronger Cadsuane is ...

Cadsuane:

Cadsuane went on. "Meilyn is considerably older. When she and I are gone, that leaves Kerene the strongest." Larelle flinched. Did the woman mean to violate every custom in one go? "Am I disturbing you?" Cadsuane's solicitous tone could not have been more false, and she did not wait for an answer. "Holding our silence about age doesn't keep people from knowing we live longer than they. Phaaw! From Kerene, it's a sharp drop to the next five. Five once this child and the Sanche girl reach their potential. And one of those is as old as I am and in retirement to boot."

This is far more definitive than Moiraine's internal whining about Cadsuane:

Even a woman as strong as Cadsuane had no right to order her here.

Cadsuane's statement makes it obvious that Kerene is well above Moiraine. In fact, from the quote Meilyn may be stronger than Kerene (hard to tell for certain). In any case there is a pretty good gap between Moiraine and Cadsuane.

Additionally there must be room between Kerene and Moiraine to fit Therava ... Galina notes that Therava was stronger than any woman in the Tower, but thinks Therava is only somewhat stronger than she is. Galina also believes Cadsuane dead so she would not count her. Therava might be as strong as Kerene or Meilyn, but from the sharp drop quote it seems less likely that Galina would consider Therava only somewhat stronger than herself if she was that level.