Look, you always need luck to rebuild.
Obviously the draft is never a sure thing and you need luck to get a good player. Luck that we haven't had for ages. (Then again, we did draft Pierce, Jefferson, and Rondo in the past two decades)
On the other hand you need luck for free agency and trades too. We've looked at our situation and decided that going all in on the draft maximizes our chances. It may pan out and it may not, but you can't say the draft is "useless" just because it's not a sure thing.