wireframe vs mockup vs prototype- Ain’t all three seem the same? They aren’t.
It is a subject that needs clarity, as it is seen differently by designers and clients.
You're right. Finished print products are very different from mockups for print. I didn't know about this either until I decided to save money on designer services and started creating designs by my own. I use free sample mockups like here https://www.ls.graphics/free-mockups/free-iphone-mockup in my projects. This helps me avoid mistakes when I prepare a new design for printing. I think that many on this site will be interested in trying these tools in their work.