Dooku can take Disney Vader and kill him before he utilizes his force abilities, and at this point Ventress can beat Barriss as well
__________________ "Happiness is a lie. Life is horror. The light is always dying all across the universe. The last star will flicker out someday, when it does, all that remains is shadow. And I will be its king!"'-Amahl Farouk
He just lacks the feats to compete at this point (assuming it's ANH Disney Vader), Dooku has beaten Kenobi, killed Ventress, held his own against Yoda, beaten Grievous, Savage etc. Hes like the 5th best duelist in the mythos, and this iteration of Vader just lacks the showings to compare
__________________ "Happiness is a lie. Life is horror. The light is always dying all across the universe. The last star will flicker out someday, when it does, all that remains is shadow. And I will be its king!"'-Amahl Farouk
Because I think Ventress will be able to beat Barriss fast enough to help Dooku. I just said I didn't know if she could do it fast enough, though I suspect she will.