I'm not using CNC; I just agree with the previous poster that there's an opportunity. (I'd note that none of your subsequent post related to the comment you made about CNC?)

For my project, I believe 19mm is plenty for carcasses - just about every mass-produced kitchen uses 18/19mm chipboard frames, and they can last for decades, outside of abnormal abuse. The main reason for using the same size is easy compatibility with standard doors/fronts together with standard fitment hinges/runners, all of which I'll be purchasing. The tops will be either granite or concrete.