>>4994913d concepting is becoming more the norm, granted 2d is initially faster but with a 3d sketch you have a POC in all angles orthographic and perspective , and that concept can be handed down the pipe easier than 2d, ironically 2015 zsummit there was a concept artist talking about this very subject, pointing out the pitfalls of 3d concepting, also old school guys like jordu schell disapprove of it, with the same complaint, a 2 hour sculpt in zbrush can easily be rendered and dolled up to look near production ready, might not be the strongest design but the polish makes it look better than it is. i agree with you that no one wants a 3d artist to concept, but they are looking more towards a concept artist that does 3d, if that makes sense, i would compare it to music, it would be easier to play someone a rough melody than it would be to write out the sheet music, 3d concepts are the same. if you have a background in concepting, and you want to use zbrush i would suggest looking up 'speed sculpts', basically if all you want is your idea , open zbrush make a primitive object like a cube or sphere and dynamesh it, then sculpt the fuck out of it. one example
https://www.youtube.com/watch?v=qV-KuHzhEvY as you can see simple shape > dynamesh> sculpt>???> profit