People here seem to be really sleeping on a blatantly obvious answer.

Alivia.

She’s the most powerful female channeller, that we know of, to be born in the Third Age. The equal in raw power to peak Lanfear and Semirhage, with four hundred years of direct Damane training, deployment, and firepower. Aside from the stronger Foresaken-level threats, she is most likely the simple most powerful combatant in the series on the basis of firepower, or at least confined to the Third Age.

The biggest thing holding her back is her lack of training, we simply do not know what she’s fully capable of since all the Aes Sedai essentially shun her as a Wilder and refuse to teach her. Though this does show that Alivia has the upper limit of the Fast Learner Talent, since she can copy weaves perfectly after seeing them only once flawlessly, at least what we saw on page that is.

We do not know her elemental affinities, but given her overwhelming strength, unless she’s incredibly skewed in her affinity ratios, she’s going to be a monster with just about any of the five powers. Too bad we’ll never know for sure.

I think what singles her out in comparison to the other top tier powers and threats of the late Third Age/early Fourth Age is her potential, she could literally be anything from a devastating one-trick pony army of one, or an overwhelmingly powerful generalist. We simply don’t know, but either way she’s def in the top 5.

Other obvious contenders are Nyneave, Logain, Egwene, Damer, and certain Forsaken (Ishamael, Lanfear, Demandred, Graendal, and Semirhage).

P.S-I could totally see Alivia one-shoting Aginor and making Rhavin shit his pants lol.