[guessbest]

You hit the nail on the head, but I'd say that things are more proprietary and thus secret than simply being archaic. For instance some places still use MARK-IV, but build out new features using Cobol. And then there is a whole field of job scheduling language like Jobtrac. It is a vast ecosystem with its own security system language like TOPS which also has it s competitors.

Also, overnight batch processing may not be automated but require an operator initializing each job in the schedule or schedule in the schedule with runsheet instructions. I think dialogs are created with ISPF and software for moving software from test to production, but I'm no expert on the mainframe.

https://en.wikipedia.org/wiki/MARK_IV_(software)

https://en.wikipedia.org/wiki/TOPS

The mainframe has a large ecosystem that is needs maintenance and feature additions and the work doesn't pay so bad if you don't mind the system. I know Mainframe DBA's make $110k in Dallas/Austin.