1 - Nobody is making David West out to be Karl Malone. Carlos Boozer is a two-time All-Star at the same position, with a similar skill set, and is a worse defender. He is making $13.5 million this year. Nene is projected to get $15+ million. In the NBA in 2011, $9 million is a steal for a two-time All-Star.
2 - Danny also has no way of knowing with 100% confidence what all 29 other GMs are thinking. If only one saw the glowing potential of JaJuan Johnson, they could have picked him or traded up to pick him.
3 - David West was also drafted in one of the greatest drafts in NBA history (LeBron, Wade, Carmelo, Bosh, etc...). JaJuan was drafted in one of the worst. It is possible that he is better than or equal to West. The chances are however very slim. Very few picks hit outside of the lottery.
4 - Jermaine only played 24 games last year. His impact is negligible. David West is not a poor defender. JaJuan might be a Taj Gibson. Odds are he isn't. Taj Gibson also didn't exactly swing the NBA title or anything. He was a role playing backup power forward who had to be taken off the floor in key situations because of his lack of offense. Even if he is Taj Gibson, I'll take West.
Also, at 6'10, with a huge size and athleticism and skill advantage over lesser college competition, why did JaJuan only average 6 rebounds per game? That is miserable. David West averaged 12 in college, 8 in the pros. Will JaJuan grab a single NBA rebound? I reference Game 7 of the Finals for evidence that we need help on the boards. You've watched him a lot, can you tell me why he can't grab a rebound?