In NYC, yes. During rush hour, the local subways come every 5 minutes at most. I think a safe estimate is about 15 trains every hour.

The express subways are spaced out a little more, closer to 8 or 10 minutes, depending on the line.

peak of the most active system is not the same thing as "usual"

here is LA for instance, about 10 minutes average during rush hour https://media.metro.net/documents/5a366ef8-2013-4d21-8e6d-e7...