> But for mass producing a solid design, 3D printing is the worst solution, because it is slow. Injection molding would be the fast (and cheap) way.

~10 years ago I was really into designing my own "drones" (but the kind that don't kill people) and I primarily used a CNC machine (Shapeoko 3).

Multirotor vehicles are a good match for designs that are a series of mostly flat plates connected via simple standoffs and you can knock those out really quick with a CNC machine.

Injection molding is certainly much better than 3D printing for scale, but CNC is a nice middle ground that allows for quick manufacture while still having a lot of the same flexibility for iterative design that you get with 3D printing.