Speaking from personal experience, it's easier to teach 3D CAD to someone who has never been taught 2D CAD. Sounds weird but the principles of building a 3D model from which you then extract engineering drawings or gcode toolpaths is fundamentally different to creating engineering drawings in 2D. Not everyone agrees, but then they might be the same people who say that "they can't get on with 3D stuff." No, not really trying to be contentious here

But I use both, and a decent 2D CAD package is perfectly adequate if you are only going to produce 2D shapes. 3D modeling and visualisation is just so much more powerful if you are creating 3D components.