“BTW I don’t buy your argument vis-a-vis the Tosafos in Yevamos. If that Tosafos held that a woman could be a dayan, it would have answered that for Devorah because it is the simplest teretz.”
Perhaps Tosafos’s starting point was that a woman cannot be a dayan and he is hesitant to change that position. If you only have the kashya from Devorah, you can easily answer that Devorah was different and keep to the original position. In other words Tosafos would only entertain the notion of a woman being a dayan when faced with the question from the drasha. Now the question is if in order to answer the other question Tosafos would say that a woman can be a dayan, would he then retract his chiluk of Devorah? I don’t think so – see the lashon of the Tosafos in Bava Kamma. It sounds to me as if he is saying that granted a woman can be a dayan as we see from the drasha, lemaaseh there is no proof from Devorah because Devorah might be different. However, I agree that the Tosafos in Yevamos definitely gives off the impression that a woman cannot be a dayan, and it is somewhat puzzling that he doesn’t address the question from the drasha.