Wouldn't there be too much error when you both 3D scan and 3D print it?

The 3d scan is generally used as a base for your cad model, you don’t print it it directly, you instead replicate the shapes in your cad software, that gives you pretty much infinite precision thanks to NURBS

https://en.wikipedia.org/wiki/Non-uniform_rational_B-spline

you'd probably have to do a bit of fixing on a model to get close

My guess is that both 3D printed fans and production fans get balanced, but the production fans have an extra bit of design, that makes the profile sail at both a wider speed range, and peaks at a higher speed.