I think the thing that you really have to believe in for Sheppard if you dig into the numbers is how he affects winning even if he's not putting up counting stats. The shooting is great and everything, but that's not his true appeal to me. For me, his superpower is being able to read the game at an elite level. My eye test is not good enough to figure out exactly how he has such a huge differential in on/off compared to everyone else on his team (+30/100 possessions), and whether that's noise or something that's translatable to the pros. Usually when something like that is the case, you think collinearity or some kind of confounding factor due to playing in more talented lineups or with another star player, but for Sheppard it's regardless of who he's playing with. That suggests that he's probably doing a lot of the little things, recognizing advantages created by opponent double teams, mismatches, knowing where to be for rebounds, making correct rotations in advance, things that probably don't show up in the box score that nonetheless have a huge effect on winning small margins.
If that's the case, that's the kind of thing that translates exceptionally well to the pros. Cam Spencer also does a ton of this which makes me higher on him than consensus, except Reed is like 4.5 years younger so he has a much longer runway to work on his two primary weaknesses: 1) a handle that is merely adequate as opposed to great, and 2) a poor ability to respond to contact on either end - he gets swallowed up by long/physical defenders and picks up his dribble or turns it over, or he dies on a screen where he is otherwise positionally very solid
He can't be a primary initiator because he is unable to make something from nothing, but he is smart enough to recognize tiny advantages on both ends and capitalize on them instantly. THat's a very powerful skill when you pair that with the soon to be best two way advantage creator in the game.