Clarke has NO shot at all, cannot handle the ball effectively, and will not be able to post up NBA pfs/center effectively due to his height/wingspan.
He will post up Guards, and he can run by bigger centers on offense, but he is relegated entirely to someone else setting him up. He cannot get anything himself.
Look, I'm the furthest thing from an expert on the draft generally, and in particular with respect to this draft.
That said, if he's so flawed and inept, how is it that he was so productive and effective this year for Gonzaga?
Guys who find ways to be super productive in college tend to translate that to the pros in some fashion, unless their game is premised entirely on size or athleticism. Doesn't sound like that's the case with Clarke.
Easiest example to think of is Kelly Olynyk, who was also super productive at Gonzaga and also has below average wingspan. Kelly is not a star by any means, nor will he ever become one. But he's been a useful NBA player from day one. He's always been a positive in the eyes of stats like +/-, on/off etc. He just helps a team win basketball games.
I suspect Clarke will be similar.