Grand Central Terminus is certainly an impressive place. . . . . .
It certainly is - especially the extensive public areas and various quirky nooks & crannies.
Total number of platforms seems to be the one measure (apart from perhaps most expansive layout located totally underground) where Grand Central wins a mine's-bigger-than-yours competition. The Guinness Book of Records says there are 44 platforms on two levels, which superficially sounds something like a "double Waterloo".
When you look more closely, many of the tracks in the station have an individually numbered platform on each side (sometimes called the
Spanish solution), which greatly increases the "platform" count.
In terms of (pre-Covid) passenger usage, I believe Grand Central had a similar volume (60-odd million p.a.) as 17-platform London Liverpool Street - although perhaps more concentrated into the two weekday peaks at GCT.
IIRC, the working arrangements at Grand Central are for many of the inbound morning peak-hour trains to just stable in the platform during the day, until it's time for the return working to the suburbs in the afternoon. This will use up a good fraction of all those platforms, and is not a practice you'd find at Waterloo, Liverpool Street or any self-respecting Hauptbahnhof.
The heavy peak-period traffic is accommodated by the reversibly signalled four-track approach viaduct / tunnel from Harlem, using three tracks in the tidal flow direction, one for the other. This works so long as you don't need to move many empty trains to/from out-of-town sidings for mid-day storage.