> It didn’t seem like 3D-printing ever showed sings of displacing existing ways of manufacturing at scale, did it?

It's really hard to beat injection molding for scale.

However, what 3D printing did shift was building molds and prototypes. And that shifted small volume manufacturing--one offs and small volumes are now practical that didn't used to be. In addition, you can iterate more easily over multiple versions.

The limiting factor, however, has always been the brain power designing the thing. YouTube is littered with videos that someone wants to build a "thing" and then spends 10-20 iterations figuring out everything they didn't know going into the project. This is no different from "real" projects, but your experienced engineering staff probably only take 5 iterations instead of 20.