Tales and Chronicles
Jewel of the North, formerly know as vincegetorix
This.London passed 2 million in the 1840s - the first city in the world to do so. Which required railways, canals and a large seaport to bring in food. A tenth of the population of the UK at the time, near enough. Bear in mind this is a city powered by coal by this time, not wood. And it was the capital of an empire that by then was global. WAterdeep is rather different - not least in not having those 21 million people living in the rest of the "country"/"area of influence".
Waterdeep is supposed to be the greatest city on the SC, but lacks any influence outside it's region.
- Compared to BG, Elturel or Neverwinter, their standing army is never mentioned as patrolling their area of influence.
- They barely(?) Have any colonial efforts.
- Despite being described as highly magiteked, the high clergy of the god of inventions is in BG where its work is intertwined with the rulership of the city.
In short, the city only feels fantastic and powerful because they bolted randomly any quirky fantasy element they could think of on the same city: a dragon in their harbor! An anti-dragon force shield! Giant statues! Spaceship! Undercity with more spaceship! Under-undercity fraught with danger but also the source of drinking water! A political system that makes no sense! A brooding edgy batman-archmage!
I think too many writers decided to add their one fantastic element on Waterdeep. Sometimes less is more.