Yeah no. I worked on mainframe code for 15 years of the last 20 and can tell you that you’re wrong. Even reasonably simple business lines have cobbled together insane cobol, batch and cics screens that would make spaghetti blush.

When you open up a 100,000 line batch program that’s just 1 of 30 cobol programs in that run which is a mess of gotos, global mutable state and basically every single other generally frowned upon software practice we know about, you start to understand the issues.

Moving off of mainframe is practically impossible because of it. That other person being voted down is actually correct, nobody in the organization actually knows how any of it works.

When organizations try to transition away, what ends up happening is they get these insane promises of “5 years” from vendors (like IBM. Ask me how I know!), but then it takes 10 years to transition single systems.

Nothing is documented. So you have business people who have no clue how anything works providing high level work flows. But then there’s always 50 random edge cases or interactions they never considered cause the 40 year old code just does it.

IT contains most of the business knowledge, but the mainframe grey beards are… stubborn. The business hangs on to these people because they’re seen as insanely valuable, not realizing that the grey beards have actually been actively suppressing knowledge to only their hidden documents, and they’ve got 8 years till retirement and are going to make sure that their job exists at least until then by actively sabotaging efforts to change. But also, for some reason, the business manager love the saboteurs. It’s insane to watch.