The term "A-GPS" in common practice includes also wifi and, as I mentioned, Google's data for this is very detailed in Manhattan, too.

Yeah, it doesn't work for this. I've tried it in the last few months and talked to people working on location about it out of curiosity. Not in NYC specifically but in other cities.

Even short buildings have issues here - if you walk down a wide street in Tokyo, which are pretty common and often surrounded by 3-4 story buildings, with the map open and look at it closely, you will often show up on the other side of the street. (Which surprised me, because it's literally why QZSS exists.)

Afaik, the issues with WiFi are that if you're traveling at any speed there isn't much time to do scans, and the position of the WiFi networks themselves isn't clear enough because of multipath (reflections), because it is crowdsourced from other devices that don't have real ground truth locations, and because the other devices gathering info are at different heights above ground or are indoors.

The main advantage of A-GPS with WiFi is that it starts up faster and that it mostly works indoors or when you can't see any satellites.