The OP makes some good points.
But I guess my reaction to this is . . . so? Of course the lottery is not a sure thing. It's not supposed to be a sure thing that getting a top pick will bring you a championship, or even that all-out tanking will win the lottery.
That doesn't change the fact that the players most likely to help a team to multiple 50+ win seasons and a chance at a title are taken in the top 5 of the draft, and by far the easiest way to get such players is to get a top 5 draft pick, and by far the most likely way to get a top 5 draft pick is to be one of the 5 worst teams for at least one season.
Bottom Line: It's a crappy system. Unfortunely, we've got to work within it.
On what basis do you claim that that is the 'easiest' way to add a Top 5 talent?
Why is that easier than just trading for 'top 5' talent?
I don't have the numbers down to the 5th pick handy, but I do know that the vast majority of Top 3' talent in the last 20 years that have gone on to win a title have done so on teams that did NOT draft them.
As stated above, only 4 #1 overall picks -- and on just 2 teams, have won the title on the teams that drafted them. No other teams other than Houston or San Antonio have had won a title since drafting #1 overall in the last 30 years. And both of them only did it after adding a SECOND #1 overall.
Only 4 teams in the last 30 years that have picked #2 have won a title AT ALL since drawing that pick. And not one of those actually contributed in any direct way towards that title. Len Bias certainly did not contribute to ours. Jason Kidd left and came back over decade later to help with Dallas' title. Darko sat on the bench for Detroit's. And finally Miami tanked only to get Beasely - whom they ended up trading for trash. They only became a title team again after purchasing Lebron from free agency.
The numbers are similar with the #3 pick.
The point is, while certainly top 5 talent is needed to win titles. The vast majority of the top 3 talent is only winning titles after _moving_ from the team that drafted it. That suggests strongly that most title teams are NOT acquiring that talent via the draft. Instead, they are acquiring it via trade or free agency.
Which begs the question if getting that talent is 'easiest' through the draft, then why aren't those teams doing so?
You will probably cite that most title teams did have a top pick on their roster that they indeed drafted. Most of these top picks have been 5-10. Often they were on those teams for YEARS before they finally won a title --- and then only by ADDING at least one more top talent via trade / free agency.
To bring this back to the Celtics - the Celtics already have several top talent pieces. Green is a #5 pick. Rondo is one of the most fantastic 'value' picks -- clearly he is lottery-level talent even though he was taken at #21. Sully was a consensus top 7 pick all the way until right before the draft when his back issues tumbled him down to us. And Olynyk is clearly a legit value at #13. You can argue about how exactly to value the two youngsters -- there are definite question marks. But so too would there be question marks of whomever we draft next year. More so, in fact.
The point is, the roster right now HAS several pieces of 'lottery level' talent.
The next step based on the historically most consistently successful model, is to now try to trade to bring in a 'Top 3' level talent.
We have a variety of contracts that can be moved. We have excess 1st round picks. Danny has all the pieces to build almost any trade package. All he needs now is a trading partner. He just has to wait until the next Top 3 talent is available via trade.