My impression was that FSP was when you had an account on a Unix server at a University and wanted to slowly move files without attracting attention

When people had their own internet connected machine other protocols were much better choices.

I always thought FXP was a much more common tool, as you could move releases between beefy servers without having to download them first https://en.wikipedia.org/wiki/File_eXchange_Protocol

I'm old enough to remember when IRC DCC fservs were a popular distribution channel.