Yea, I think a good concept artist is really essential here. And of course a good concept… I mean, if you have some good pre-production art to show off your ideas then people are more likely to jump on-board. It speaks volumes more to a team then throwing a GDD at people and expecting them to get excited. I think the “idea” person can typically visualize their ideas, so it’s easy to get excited about it. Well, putting those visuals on paper will help other people to get excited too. As they say, a picture is worth a thousand words.