I was a mainframe programmer for a few years when I started out in IT and I must say your observations are quite correct.

First, MF batches tend to be very straightforward. Basically, they're a chain of modules, each with their in- and output, linked together and to the environment with JCL.
The only thing that changes tends to be the data stream

Secondly, there's no code re-use - or at least not enough.
If you're lucky, the record descriptions you need to use are located in a library - and that's the end of that.

It took me quit some time -and the help of others- to come to terms with "the new ways" of programming...
Lotus Notes introduced libraries and code-reuse to me, Java the concepts of API's and OOP...
And then there's Perl.<GRIN>

The shift was a lengthy process... but worth it!

Cheers,
MichaelD