Semantics. There are all kinds of "mistakes." The example you give is one. A "poor choice" that produces an outcome that the actor did not intend is another type of mistake. See, e.g., Merriam Webster, Oxford, and Cambridge: "an action or decision that is wrong or produces a result that is not correct or not intended."
My wife and I go to a restaurant. We are torn on what to order: I order the short ribs, she orders the black cod. Both look like good options; I'm honestly not sure which one is going to be better. Turns out my short ribs are overcooked, dry, and one-note while her black cod melts in my mouth like butter while my taste buds explode in a simultaneous orgasm. She made the better choice. Did I make a mistake? Depends on how you define it. Poor choice. Yes. Was that poor choice a "mistake?" Absolutely. I certainly desired a better experience with my meal and would have had that experience had I not chosen poorly.
Same scenario with a twist: My wife and I walk into that same restaurant having done our research. Both friends and critics alike agree that the black cod is one of the best seafood dishes any of them has ever had. But I don't feel like seafood. I want something heartier, so I still choose the short ribs because that's what I feel like that night. I think it probably will suit my palate better. But I was wrong. I made a mistake by not listening to the experts.
Twenty/twenty hindsight teaches us that the Jazz made a terrible mistake drafting DWill instead of CP3 no matter how you characterize it -- exacerbated by the fact that most experts agreed that CP3 was the better choice.
As for the semantics debate we seem to be having, I chose to characterize DWill as "arguably the biggest draft mistake in Jazz history" in my OP, but could have easily said he was "arguably the poorest choice of any draft pick in Jazz history." Either way, I stand by my post.
