I am not getting that teams that ended up with picks that were 5th or 7th or 9th or 10th are conclusive proof of a team that tanked. I remember some of those teams. They didn't try to lose on purpose, they just were bad and ended up as the 5th or 9th or 10th worse record that year. There is a difference.
With enough indirect correlations, you can make anything look like a tank job. 
And with enough hindsight like some people are using here.
Like this Wade talk: Wade was not a Duncan level prospect. He was very promising but I don't think people were saying "this is the best SG of his generation" coming out or anything close. (EDIT: just quickly looking at all the old draft info on him, there was a huge concern he couldn't shoot and further that he was a tweener and had no position. Too small to be a SG).
It's all so vague, so it makes it kind of impossible to argue about. Technically though, that was a tankworthy draft with people loving all of those top 5 players, the Heat tanked that year and it lead them to 3 championships.
Ok. So let's go with the Duncan year for a minute. Should we conclude that because the Spurs tanked for Duncan and got him and then won that tanking works? Or should we conclude that the team that had a much better chance of getting him (the Celts) didn't get him and therefore that tanking doesn't work? Also there were other teams in that draft. The ones that got Tony Battie and Keith Van Horn and Anthony Daniels and Tracy McGrady. Tanking didn't work for them.
Do we conclude tanking works because one team got one player, or do we conclude it doesn't because of the experiences of the other 7 teams?
The Heat. They weren't tanking for Wade. They were tanking for Bron like everyone else. It was just as possible for Wade to go to Cleveland to play with Bron as it was for Bron to go to Miami. In the event they got the 2nd pick or the 3rd they were probably going to go with Melo or Darko, or maybe Bosh.
Wade simply doesn't get a ring without Shaq or Bron. He is incidental to a ring, not the cause of one. He's Scottie Pippen at best. He's not Jordan.
They tanked in a loaded draft --> got a world class talent from tanking ---> other world class players like Shaq, LBJ and Bosh decided to join up with another superstar --> lead to 3 championships.
Tanking is not the end all be all, but it is a great shortcut to put you in position. It doesn't have a 100% success rate, nobody is saying that, but you can throw in the towel for one year and have a dominant team from it. It is in fact easier to tank to get a good player than get a good player in free agency. Trading for good players is more reliable, but you need to essentially semi-tank to get the assets needed to trade for the good player in the first place.
What works better than tanking for winning championships? Most championships have been won by being a FA destination, tanking or both. It's hard to look for success stories without one of those two factors being there and we're not an FA destination. I am a little more optimistic about us getting FAs going forward, but it's hardly a lock.
My point is this: instead of looking at all the teams that have tanked and seeing how many of them have won championships, look at it the other way. How many teams that have won championships tanked for one of their key players? The answer is at least half of them. The Bulls lost 14 of their last 15 games tanking for Olajuwon, but they still liked MJ leading up to it. Tanking for a top 3 pick in a good draft class is still tanking even if you like the #1 pick the most.
Edit: Also - to be clear - I don't want the Celtics to tank going forward. I just can't fathom how people don't think it works.