> Hopefully the author doesn't go down the rat hole of setting up Hercules with a 1970's era version of MVS operating system, and tries to learn enough JCL to execute the compiler. That's truly a waste of time.

Why? Cobol, JCL, RPG, ..., run on modern IBM MVS (OS/390, z/OS), unmodified. If someone seeks to learn IBM mainframe systems internals and don't have access to modern software, Hercules-390 and MVS 3.8 it's a viable option to get started as an application or systems programmer.

IBM has its own turnkey system called z/PDT so you can run a mainframe on your laptop, something that Hercules-390 can do too.