Illustrator might be precise enough for the leather work that we do. It is capable, so by all means, use it.
But AutoCAD is objectively more precise. Down to five decimal points of any unit, if I recall correctly. It's why you simply won't see engineers and architects using illustrator. In some of the work I do - CNC, manufacturing drawings, and architecture, Illustrator just won't cut it.
Depending on the drawing It's also, at least for me, far quicker to draw in AutoCAD. If it's a simple pattern, I might just start in Illustrator if that's the end format I need. But if I need an extremely precise drawing and it's complex, it will be far faster for me to start in AutoCAD, and move over to Illustrator later for colour fills and other things it's better at.
Which brings me to: different software excel at different things. No one balks at moving in between photoshop (raster) and illustrator (vector). And you likewise shouldn't be afraid to move between Illustrator (illustration), and CAD (drafting). If you haven't tried AutoCAD yet, I encourage you to. Certain operations are unwieldy at best in Illustrator like arcs, offsetting lines, dimensioning, and until recently rounded corners. These are extremely easy in CAD software.
Back to the point though! In the case of this project, CAD software is unnecessary - dies don't need microns of precision. But, bylinesupplyco was having trouble doing the pattern in Illustrator so I simply I thought I'd mention AutoCAD as it is more purpose built for drafting, and might be easier for them to learn for that purpose.