A file server is a pretty basic task, and zfs is a pretty good choice of fs for a file server, and zfs wants all the ram you can scrape up.
But still there may not be many such examples so your point is still valid.
I use a 3b+ for a 3d printer and that means, octoprint, klipper, octolapse, live streaming from a webcam while printing, a web server and web ui with various plugins, a slicer (I don't slice on the pi, but it's there and I could) and for all that the 3b+ is hardly scratched while running full out. It's a 4g model that is always using only couple hundred meg if you don't count disk cache. This is exactly consistent with your supposition.
But still there may not be many such examples so your point is still valid.
I use a 3b+ for a 3d printer and that means, octoprint, klipper, octolapse, live streaming from a webcam while printing, a web server and web ui with various plugins, a slicer (I don't slice on the pi, but it's there and I could) and for all that the 3b+ is hardly scratched while running full out. It's a 4g model that is always using only couple hundred meg if you don't count disk cache. This is exactly consistent with your supposition.