Exactly. 3D printing makes an approximation of the 3D space occupied by a given part, and nothing more. For some parts this is sufficient, for most it is not.

There is a whole history of materials science and production techniques to get to the 'stuff' we have today, 3D printing is rather 1 dimensional in comparison.

This comment goes a bit too far the other way. 3D printing is a manufacturing technique with its own possibilities and drawbacks which you need to be aware of, but it's very possible to make engineering-grade parts with 3d printing - for some things, it's even the state of the art. You can eliminate layer stress lines with annealing, and you can print interior shapes that would be impossible to injection mould. I myself have made polycarbonate fan blades, only a few mm at the thickest point, with a tensile strength tested to over 500 kilograms. Their theoretical strength is much higher still.