Baenre is THE most prominent house in Menzo, so Minthara is from there. The fact that she even says that she would bring us there as her consort further solidifies this.
As far as it being the greatest Drow City, the only reason it is considered this is because it is so popular in our world. Once upon a Time, R A Salvatore wrote some books because he was creative and had developed a culture and society for drow. It became so popular that now everything has to be about that one city when Drow are involved.
Now, I will say that it does seem that it will likely be imperative to the overall story that it is Menzo and not some other City. After all, you are correct. If Minthara hates Lolth and serves the Absolute, then if she is going to take Tav as her consort back to Menzo, then it is likely that Menzo has fallen to the cult and is likely a major player in the overall story. My hope, then, is that they at least explain how a city hundreds of miles away is so involved with the Western Heartlands.
