I don’t think COBOL does force you to mix concerns. You could create sub modules / services which you call from a main program to do things like file writing or database reading.

Java doesn’t also say you have to separate concerns. You could easily write a single method which mixes business logic and IO (file and DB)

When writing a batch program you need a balance between understanding it, making it efficient and reliable and promoting re-use (e.g. if many batch programs want the same behaviour break it into a reusable module). COBOL still has dependencies too, so each program is rarely written in isolation and you have to co-ordinate with other teams to ensure their module versions are in sync with yours.

The thing that has always let COBOL down for me is the lack of automated testing.