Rajon Rondo is:
1. A veteran with nearly 100 playoff games, including 2 finals and one championship, under his belt;
2. A player who has consistently elevated his game in the postseason, in nearly every aspect of the game;
3. The only clear matchup advantage we have at any position vs. the Heat;
4. Someone who has a proven ability to take over and win a playoff game by himself.
Sullinger is none of those things. He has half a year of NBA experience in which he has proven that when healthy he is a capable NBA big man. He averaged 7 ppg and 7 rpg in 23mpg in his last month of NBA hoops. These are average numbers for a quality backup PF/C. He has not proven that he is a clutch performer, either in the regular season or the playoffs.
Do Rondo's 40 games at the beginning of this year prove that he had regressed? Maybe - but maybe not, we've seen him go through slumps before. And he has always elevated his game in the playoffs. In fact his playoff numbers last year were his best ever by most metrics.
The discussion about whether we were better or worse without Rondo is completely empty. The sample size is too small. Too many other players were moving in and out of the rotation. It is a noisy, apples-to-oranges comparison in which one learns nothing of value.
So, the best evidence we have to go on is the longer history. Rondo's playoff history, and his unique advantages vs. many of the teams we fear most, are facts.
Sullinger has no history. In the absence of any history you have to ask what are the odds that Sully could elevate his game enough to be the best player on the floor for an extended part of or maybe an entire playoff series against one of the best teams in the NBA, as Rondo has done repeatedly. Heck, Sully never even established that he could stay on the floor as a rotation regular - in his last 14 games he fouled out of 6 and had 5 fouls in two others - in 23 minutes per game!
If anyone really thinks that the odds of Sully morphing into someone who could lead the Celtics through an NBA playoff series the way that Rondo has done, well then, you are entitled to that opinion. Just recognize that your opinion is contradicted by nearly all of the facts that we know about these players.