You are assuming that vector design can't be 3D-ish.
The parent is refering to the fact that it's much easier to make a design work on more resolutions with vectors.
I am more pointing out that it is not so black and white, since designs can include images/bitmaps/patterns etc so just saying "svg it" doesn't really cut it.
But yeah, it is easier to make it work and it can be non-flat as well.