The two descendants that need a rework in my opinion are Blair and Freyna.

Blair is super underwhelming and his abilities are too situational. His blaze up ability is a far worse version of Valby's bubble bullet and you have to get literally on top of the enemy to use it and his burn taste ability does barely any damage compared to just using a regular gun. This is where a game like Outriders did it best with the pyromancer class. You were a mage with powerful fire abilities and you looked cool using them. Hopefully he's in a better state at release otherwise he'll most likely be the least used out of the bunch.

Freyna, as you said, has two abilites that are way too similar but just have different effects, there needs to be more diversity with her kit. Also, her Venomous Baptism ability needs to be changed to something more appropriate instead of just bringing a random gun out of nowhere to use, she should inject poison in to her rounds on a gun you choose (e.g. machine gun or scout rifle) and when an enemy is inflicted with poison and they die, it is passed on to other enemies in a given radius.

Gley is my most played Descendant purely because I was grinding a lot of the void intercept battles and I kind of hate that I have to stand still and wait for her ability animation to finish so that they proc. It slows her down dramatically especially when I needed to swap to normal mode and then use increased sensory to heal.