Ie. a route with 4 stops and a travel speed of 100 mph.
The finances of railways actually get better with faster trains - because the sooner you can get the person to their destination, the quicker you can get that train serving another passenger.
It's definitely under capacity by that metric.
https://www.wnyc.org/story/subway-ridership-hits-65-year-hig...
The only issue is that then it arguably had a much larger tax base than it does now to fund it.
I mean when were these built, a 100 years ago? Surely there's room for improvement.
Because building a subway in New York City costs $4 billion per mile.
"The Trains Are Slower Because They Slowed the Trains Down"
https://www.villagevoice.com/the-trains-are-slower-because-t...
Similarly there's a top speed of 79mph on the rest of the country on most passenger rail since the Naperville Train Disaster of 1946
It's the blue+yellow line which goes off the east side: https://content.tfl.gov.uk/london-rail-and-tube-services-map...
I don't think that's unusual for very large cities with high speed trains. The longest-distance trains probably only stop at one station in each city, but medium-distance trains can stop at multiple.
I've never come across a metro train travelling that fast though. The cost of building the line to support those speeds would be tremendous for a small difference in journey time.