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.
Bingo. It certainly
regionally important originally, but it wasn't necessarily uopposed even in the North. Notably, it's sister city, Ched Nassad was larger and more prosperous and conceived as a rival/ally of sorts. Menzoberranzan wasn't the oldest city, being a third-generation founding, nor was it the highest in Lolth's favor.
Other notable cities besides Ust Natha, Shamath, and Ched Nassad that were mentioned previously include Guallidurth underneath Calimshan, one of the oldest drow cities and likely the most populated, an entire species of sentient creature, the Aranea was likely created solely to fight the threat this city poised to the surface. There's also T'lLindhet, another old city, not as heavily populated, but the only one to rule over holdings on the surface, in this case the nation of half drow, Dambrath.
But because of it's popularity, a lot of retcons and story developments have happened that have drastically changed what Menzoberranzan is in relation to the drow. Ched Nassad was destroyed, Dambrath destroyed in civil war, Guallidurth purged in religious infighting. Menzoberranzan was written as more and more powerful both in the present and past tense and other drow cities were written about less and less. Now recently WoTC rewrote drow and elven history, making Menzoberranzan the founding city of Lolth's religion, and throwing up the canonicity of other drow cities into question.
Rather unfortunate evolution, IMO. Now of course, Sshamath gets a mention in BGIII, which is great because It's always been a city I'd like to see more of, but the glut of mention Menzoberranzan gets in the game by comparison makes more sense in that context.
