Ainge himself has said they are looking for championship caliber players. Monroe is not a championship caliber player.
Ask yourself this question:
Can Greg Monroe be a top 3 player on a championship caliber team at center or PF?
The answer is no.
If you think Sullinger is, will be, or can be traded for a top 3 player on a championship caliber team (at center or PF), you're a lil' out of touch with reality.
Sullinger is in his 3rd year. He's played less than 2 seasons of NBA basketball because of his back injury. In his 3rd season, his numbers are better than David West, Greg Monroe, Zac Randolph, Taj Gibson, Josh Smith, David Lee, LaMarcus Aldridge, Carlos Boozer were in their 3rd seasons.
He currently isn't good enough to be a top 3 player on a championship team- but this is also his first season playing power forward in the NBA. His sidekick is Kelly Olynyk who is not a traditional center which is a huge disadvantage on team defense and help defense. Give him 2 years in the NBA and he's likely going to improve even more.
If you don't think that Jared Sullinger can be a significant piece in a trade for a star at some point, then you sir, are out of touch with reality.
He's an excellent player and of all the third year players in the NBA, and it's fair to say he's a top 5 player from the 2012 draft who we picked up with the 21st pick.
2012 draft best players:
Anthony Davis pick #1
Damian Lillard pick #2
Andre Drummond pick #9
Jared Sullinger pick #21
Bradley Beal pick#3
He's also one of only 4 power forwards in the NBA to average more than 15 points a game and shoot 35%+ from three.
Those 4 players are:
Nowitzki
Love
Ibaka
Sullinger
Assuming he can improve his free throw percentage to above 75% (currently at 68%), he should post per 36 numbers of AT LEAST 20 points/10 rebounds by the end of next season.
He currently posts per 36 numbers of 19.5 points and 10.1 rebounds.
If we get really lucky and he becomes a 40% 3 point shooter and shoots 80%+ from the line, he'd possibly be a 22 point, 10 rebound monster with stretch ability that can guard the PF and Center positions when needed.
In other words, he is projecting to be a better player than David West was as an All Star in 2007 and 2008 averaging 19.3 points and 7.5 rebounds per 36 minutes a game- and West had Chris Paul and Tyson Chandler on that team to help him on defense and get him the ball at his favorite spots. (which Rondo does a good job already with Sullinger. Olynyk does not help guard the paint like Tyson Chandler. lol).