In what Celtics world is Rondo not a superstar?
Guys I might consider including:
Zach Randolph 3x (Por to NY in '07, NY to LAC in '08, LAC to Mem in '09)
Shaq 2x (Mia to Phx in '08, Phx to Cle in '09)
Tyson Chandler 2x (NO to Char in '09, CHar to Dal in '10), this could be 3x or 4x if you want to include '06 and '14 too.
Marcus Camby (Den to LAC in '08)
Shawn Marion (Pho to Mia in '08)
Jermaine O'Neal (Ind to Tor in '08)
Al Jefferson (Min to Utah in '10)
Gerald Wallace (Char to Por in '11)
Monta Ellis (GS to Mil in '12)
Eric Bledsoe (LAC to Phx in '13)
Jrue Holiday (Phi to NO in '13)
Luol Deng (Chi to Cle in '14)
Rondo (Bos to Dal in '14)
Reggie Jackson (OKC to Det in '15)
Goran Dragic (Pho to Mia in '15)
Roy Hibbert (Ind to LAL in '15)
Sure some of these guys you might look at and think, superstar? Am I crazy?
The thing is, there's such a loose definition of superstar, and it's easy to nail down in hindsight. But at the time of those trades? James Harden had never been an All-Star or All-NBA when he was traded, we know he's a superstar now, but he could have turned out to be Jrue Holiday or Eric Bledsoe or Monta Ellis or someone like them. I bet OKC definitely didn't think he'd turn out to be so good. Reggie Jackson could turn out to be the same way (definitely had a nice run in Detroit).
A guy like Deron Williams hasn't been All-NBA once since becoming a Net, not a superstar in my book since the trade (but at the time I would have said he was one).
When vets like KG or Ray Allen are traded, nobody really knows how much they have left. Sometimes you get what KG was in Boston and sometimes you get what Jermaine O'Neal was since he was a Pacer.
All the guys I included above (and I'm sure there's more if I really think about it), sure they aren't superstars now (some still have the potential to become), but for the most part they were coming off All-Star/All-NBA years or were averaging either 20+ points or 10+ apg or 10+ rpg (or some combination thereof), or were maybe just a season or 2 removed from doing so. They're all guys that still had All-Star, All-NBA, or DPOY potential at the time of the trade.
Very few superstars are traded because well there's very few superstars (and even fewer who are on losing teams looking to leave town). But you can somewhat easily trade for a player capable of making an All-Star or All-NBA team.