Overpay. I think you might be underrating Zeller and definitely Bradley.
I'll expand on this a bit because I like your idea.
I'll put as much of the value of the assets in question in terms of draft picks so it's easier to follow my thinking.
Earlier this season teams wanted a 1st rounder to absorb Lance Stephenson. Now a full year of his contract is off the books, but he arguably worsened his value by showing for another half of a season that he's nowhere near the player in Charlotte that he was in Indiana. So we'll say he's worth a negative late first round pick.
Also earlier this season there was a thread that was started (if someone could find it, TP to them) polling the value of Tyler Zeller. Almost everyone agreed he was worth a 1st rounder from 10-15. This was before he became our permanent starting center and the team pulled off a pretty incredible playoff push. I don't think Danny's parting with him for anything less than a pick in the 12-14 range.
It's as hard to put Avery Bradley's value in terms of draft picks as it is for Celtics fans to agree on his value. I'll briefly defend AB. Bradley had a 4-game slump at a poor time. But the big picture still shows AB as at least an average starting caliber SG at just 24. This year his 3 point field goal percentage dipped from 39% the previous season to 35%, but Avery was asked to shoot a greater percentage of his shots this year from 3, shooting 4.6 3s a game compared to last year's 3.3 average. His 2-point shot percentage actually improved, and most importantly, his shot percentages by area have shown he's grasped how to exploit his strengths on the offensive end. Avery recognized that he was poor from 3-16 feet, so this year he took 5% less shots from that range, while still maintaining a sizable reliance on shots at rim and long 2s, and took over 10% more of his total FGAs from 3-point range. Presumably he only took good shots from the 3-16 foot out area, as he increased his FG% from this area by 7%. Taking a lot of layups and more 3s than ever is not Avery playing outside of himself -- this is just him practicing better shot selection. Conveniently for the Celts, this is where the game is headed: layups and 3s.
Long story short, Bradley sustained double digit scoring and above average 3-point efficiency on a much better team than last year's with relatively minor statistical decline. His offensive game, while largely tapped out, still appears to have some potential left and he's certainly squeezing every drop out of it. I would imagine at 26 or 27 he will certainly be an above average starter on the offensive end. Pair that with his defensive ability -- which he showed a recommitment to this season (that, I think, needs little explanation) -- and you've got yourself a pretty good player. Certainly a much better one than Lance Stephenson has been with the exception of one season (of which we are a full year removed from), and one that I think we can safely assume is worth a pick in the 12-14 range as well (loose basis: George Hill for #15).
Thus, the Celtics are agreeing to:
#16, #28 or #33, a late 1st by taking Stephenson, a late lotto pick by giving up Zeller, and another late lotto pick by giving up Bradley
for
#9
That's just too much for me. I would much rather do:
#16, #33, #45
for
Stephenson and #9, using the Rondo TPE to absorb Stephenson.
We move up with #9, 2016 BRK 1st and Evan Turner (probably surprisingly valuable right now) to #5 or #6. I'd be willing to part with the LAC pick as well. Select Justise Winslow. Then sign Greg Monroe as Who said.
Smart/IT
Bradley/Young
Winslow/Crowder
Sully/KO
Monroe/Zeller
Strong looking team.
edit: I'd probably look to cut ties with Stephenson ASAP unless he showed immediate commitment to returning to his level of play with Indiana. That team doesn't need him in his current state.
Well, to me I think that overvalues Zeller for sure, but I'd give you that value for Bradley. In my opinion, Zeller is worth a pick in 20 range or lower.
My issue with Bradley is that I don't think he'll be able to survive long-term with Smart, who I'm much more committed to. Smart isn't a pure ball-handler, and Bradley can't handle the ball safely for more than two or three dribbles at a time. He's a perfect complement kind of guy for a Rondo-type, but not Smart. Stephenson (if nothing else) would keep Bradley's defensive chops with extra size, while also providing the ball-handling to aid Smart, who I think will take a much more proactive role in the offense next year.
Stephenson is still 24, and he was criminally misused in Charlotte this year. So I don't think you can go as far as saying he's worth a negative first round pick. You're paying for potential that he's already shown, and it's just a year's worth of salary if nothing else giving us supreme cap space in 2016.
Plus, the gap between the #9 pick (WCS, Hezonja, Johnson, Porzingis) and #16 pick (Booker, Looney, Portis) is a huge one this year. I'd argue that the draft pick gap plus Stephenson's already shown potential is worth gambling for with our pick(s), a 3 and D guy, and a reserve big.
We'll agree to disagree on Zeller, or if you'd like, compromise and say he's worth a pick in the 17-19 range. Celts still give up way too much in your original proposal.
I disagree about Smart's ball-handling. Smart was plagued with a bum ankle ever since that nasty sprain earlier this season. As the season went on and Smart grew more explosive we saw him drive to the rim more. I thought he was very in control on those drives. Even if you think he'll only ever be an average dribbler, his elite body control, superior size and advanced court vision help to negate a lack of sophistication (combo dribble moves) about his ball handling, as he can shield defenders and create space with the former 2 traits while outsmarting (ha) opponents with the latter trait. A good indicator of his ball-handling skills would be to compare his ball-handling turnovers with another player's. This year Smart had 16 turnovers off the dribble, while Elfrid Payton totaled 42. Now, Payton played 97% of the season at PG while Smart played 74% of the season at PG (1.31x more), and Payton had a usage rate of 18.3% compared to Smart's 15.1% (1.21x more). Payton also played in 82 games compared to Smart's 67 (1.22x more) and in those games averaged 30.4 minutes compared to Smart's 27 (1.13x more) Even mathematically accounting for that (16 x 1.31 x 1.21 x 1.22 x 1.13), Smart only would have had about 35 turnovers. There are other things that are difficult for me to amateurly factor in, such as game pace, or teammates (Who is the better 2nd ball handler, Turner or Vic Oladipo?). But I think it's safe to say that everyone believes Elfrid Payton will be a competent PG, and I can't think of any other unaccounted for factor that would multiply Smart's turnover total to a number significantly more than Payton's 42.
You're being overly optimistic about Stephenson's ability. It's hard to be misused as a perimeter defender and there's not much to indicate that he was the same defender this season that he was the previous one. It's quite possible that he just benefited from playing alongside Paul George, David West and Roy Hibbert within Frank Vogel's system. Perhaps a better way to describe his defense this season is that he was used fantastically by Vogel and the Pacers and now has to fend for himself every night on the defensive end like the majority of the NBA's players, including Avery Bradley post-Pierce/KG. This season Stephenson proved to us that he's not much more special than a lot of the league's good-could-be-great-with-a-shot-blocker perimeter defenders.
Offensively, he just stunk this year. His wild card shooting ability would be challenging for Stevens to integrate on a team that figures to keep Crowder, Smart and possibly Turner, and hopefully add an athletic big man (not many of those that have shooting range). He's had two good shooting seasons and three really bad ones. Meanwhile Bradley has had an eFG% of 44% for 4 straight seasons, 3 out of the 4 (including this season) equal to or above 49%. The upside would be if Stephenson could bounce back and provide superior passing and rebounding. That is understandably desirable. Ultimately, however, this is what it comes down to in terms of on-court value (ignoring financial pros and cons): absolute best case scenario, Stephenson is a good but certainly not franchise-changing upgrade over Bradley; realistic bounce back scenario, Stephenson is as impactful as Bradley is right now (not factoring in any improvement from Bradley); expected scenario (stays the same), Stephenson is a downgrade; worst case scenario, Stephenson is $9m sitting on the bench and souring the team. The upside is simply not there to justify the risk.
You're also being overly optimistic about his contract: By the time Stephenson's contract expires and Bradley has one year left on his deal, isn't it the consensus that the cap will be over $100m? I'd rather have a guy we know is a capable starter on a $9m (ridiculously underpaid at that time) expiring contract vs. $9m in extra cap space when we could already have an obscene amount that summer if we structured properly.
Final point on Stephenson: You say that I can't say he's worth a negative 1st round pick because
you like his upside more than any other GM in the league does. There is near definitive evidence that the cost for absorbing Stephenson before he proved for another half a season that he's not all that good was a 1st round pick. If anything I'm being generous by characterizing that pick as a late 1st rounder. Even if you believe more than any other league executive that Stephenson has it in him to bounce back, it'd still be a bad move to give up more than you have to (or in this case, take less than you could) to acquire him.
I also disagree about the differential in pick value. I doubt Porzingis and both of Hezonja and Johnson are there at #9. I think the draft falls off around #6 and following that there's not much difference between picks #7-20ish. In some mocks Myles Turner is falling all the way to 16. Devin Booker is a strong prospect, I'm not sure we won't look back on this draft in a few years and shake our heads at our refusal to move him up the draft board, much like favorites of mine in the past (Klay Thompson, Kawhi Leonard; but I'm not bragging, I also loved Hasheem Thabeet

).
I like your idea because I didn't even think of Charlotte as an ideal partner to move up, whether we want to stay in the 8-10 range or use the acquired pick to further move up. Stephenson's contract makes so much sense and we have the ability to absorb it. But the possibility of Stephenson bouncing back excites me far less than it seems it does you, which is why I think we're overpaying for the return you suggest we target. And after two posts and an unnecessary amount of paragraphs, you know why I think that.