What little I know about the MH type mail stores and associated utilities are indeed quite powerful.
I think they operate under the premise that each message is it's own file
and that you work in something akin to a shell if not your actual OS shell.
I think the MH commands are quite literally unix command that can be called from the unix shell. I think this is in the spirit of simply enhancing the shell to seem as if it has email abilities via the MH commands. Use any traditional unix text processing utilities you want to manipulate email.