[jmt_]

Yeah, this is the exact sort of thing I was picturing. So for, say, a recent CS graduate, the common methods of, say manipulating files/data e.g file descriptors, sockets, databases etc, don't seem to really apply within the kind of environment you describe, which makes me question how much knowledge a 'typical' programmer can easily port over to working on real-world COBOL systems or at least how fast said programmer can start making meaningful contributions to the codebase. I'm not sure how much effort any given company looking for COBOL devs would want to invest in teaching new programmers how to work in the environment and are probably preferring people who already understand the mainframe they're using, which would exclude most working developers. Even if the company is willing to teach you, that skillset probably won't be useful at your next job, unless you want to start a career as a COBOL dev.

tl;dr learning COBOL as just a programming language doesn't seem to prepare you for an actual COBOL job in most cases, unless the company is willing to invest in teaching you.