"With the 5th pick in the 2012 NBA Draft, the Sacramento Kings select Harrison Barnes, forward out of North Carolina."
And the fans are hopeful. And the coaches are hopeful. And Tyreke Evans is hopeful. And it is good. For a couple of months.
The fact is that no matter how good Harrison Barnes ends up being offensively, he doesn't figure to greatly aid the team's defense directly. He can help it a good bit indirectly: Evans is a strong defender with the potential to be an elite defender ... at two-guard or point guard. Drafting Barnes moves Evans into the backcourt on a more permanent basis. It also figures to drop Marcus Thornton's minutes some; Thornton and Isaiah Thomas make up a pretty bad defensive backcourt, so there's another indirect bonus.
But there are still defensive holes, including an assumed one at small forward. And as we well know, this team's primary deficiency is defense. The shooting is poor, too, but the defense is just awful. That's the problem with picking Barnes instead of a defense-minded big man: it doesn't address the team's gaping hole.
Subscribing to the Best Player Available principle means that you don't totally care about that. It'd be better to have a nice small forward that didn't solve problems but has value than a busted big man that didn't solve problems and has no value. So it should go with Barnes: he'll pan out to some degree, but won't solve the team's structural problems, and the front office will do what the front office does and try to paper over it by conceding one of the team's other assets. And the cycle continues ... unless Barnes legitimately becomes a star, rising with DeMarcus Cousins and carrying everyone else along for a ride. In which case, we're back to the 'perfect world' scenario.
Most likely, the team will get a good return on value by picking Barnes, but a good return on value just won't be enough to push the team far enough to make the playoffs anytime soon. Yes, the most likely result is not very awesome. :-(