As a result of this lineage it also has quite frequent stops, which are easy to put in when the subway is just a stairway's height beneath the street. To give you an idea, the 1 line stops at 14th, 18th, 23rd, 28th, and 34th Streets. That's five stops in one mile.
This table has the subway at the world's ninth oldest, which is definitely still one of the oldest considering there's hundreds now: https://www.worldatlas.com/articles/the-world-s-oldest-metro...
As a tangent, London is adding overground trains as part of its expansion. The Overground is pretty recent (and it shows) as is the fully-automated DLR, and now there's a Crossrail making an appearance. NY hasn't invested in a hell of a lot in overground infrastructure and it feels like that's a logical step in the outer boroughs.
Quick Wiki search indicates NYC has about 1,112 km of rail vs Stockholms 105.7 km. So about 8-9 times the distance