Having worked with "spreadsheet stacks" for the last two decades I'd argue that although they can be effective in most cases they are error prone which is the point being made in your quote. And they become more error prone the more complex the "system" is and that's bad news because it's oh so easy to add more complexity whenever you want.

I agree the practices described don't sound strange - they sound normal, but so does the resulting errors that occurred - also par for the course.