One thing is that you don’t need fancy tools like 3D printers for prototyping. You can go a long way with just simple tools and materials. Yes, a 3D printer makes wonderful shapes and stuff, but you can do the same thing with knives, balsa wood and clay.
Back in 2003 Canon put up a tutorial on how to block out a camera prototype in balsa wood to test look and feel. They have since pulled the tutorial from their website but I found a more or less complete copy.
Does anybody remember the old erector sets? Well you can get kits to do the same sort of stuff. Expensive ones. If your prototyping transmissions and linear motion these are big time savers. That’s important in product development.