It wasn't a weak draft at all. And even if it was then that would mean there were a lot of bad picks and he was one of them.
It's very easy to name 3 guys picked after him we'd rather have by a ton and a couple others that are better difference makers or just better.
You also have to ignore that Steven Adams was picked one pick ahead of him. Pretty huge drop off
It may be easy for you to name three guys picked after him that you'd rather have "by a ton," but that would be based on fairly subjective criteria I suppose.
He's 9th overall in VORP in his draft class and 8th in WinShares. Not world beating, but a solid pick at his position.
I also happen to think he's not done improving. That may sound weird in a sport where lots of kids hit their peak at 23 or 24, but Kelly just strikes me as a classic "late bloomer." My guess is he learns to maintain he s mental focus better and stay more emotionally even keeled on the court as he grows older and gains more experience. This will help him be a more consistent pro.