The difference, as I recall it (and it's been decades), is that VMS HELP tries to display all of the commands in a curses-like screen. That kind of works for a few hundred commands, but not thereafter.
Unix has things like 'man -k', but those ultimately output into a pager, which is well-designed to deal with quite long lists.
I do miss HELP and EDT, but they're hopelessly outmatched by modern tools.
