Stop it. Lee had a nice preseason game and Sullinger is fat. Lee is pleasing us and Sullinger is disappointing us. We're all on board with this, now keep a clear head for a second.
Lee is a great passer. Sullinger is a great passer who actually turns the ball over less than Lee does.
Lee is a good rebounder. Sullinger is his equal.
Lee is among the worst defenders in the league at his position, a distinction he carried even in his athletic prime. Sullinger is a passable defender, in all his rotundity.
Lee is a decent finisher and gets about 54% in the paint. Sullinger is his equal.
Lee is an ok midrange shooter. Sullinger is a good midrange shooter.
Lee never takes three pointers. Sullinger jacks them up all the time and oh my god I just hate his stupid face.
Neither one draws fouls.
Stop making me defend Sullinger. ARGH!! David Lee is not that good any more, and he was super flawed in his prime. David Lee is OK and can help us and that's wonderful. You are blinded by the fact that he is not Gerald Wallace and not fat!
I think most of the things you said here are true, but I do think that Lee is more mobile than Sullinger, and he has the edge mentally.
The most important thing here, though, is that Lee can realistically play 24-30 minutes with high energy, while Sullinger has never shown an ability to remain consistent over a whole game, playing that many minutes, over the course of the regular season.
One major difference you're glossing over here, though, is that Lee is a much more efficient offensive player. Sullinger has hovered around 50% True Shooting for his career, while Lee has been around 55% the last handful of seasons, and 57.5% for his career.
True, Sullinger has shown greater range, but he has not consistently been able to utilize that range, and Lee has been just as capable of helping an offense put points on the board regardless of his lack of range.
At the end of the day, I don't think either Lee or Sullinger is a quality starter at PF in today's league. Lee is a better version of Kris Humphries at this point in time, and Sullinger is a significantly worse version of David West, albeit with an occasionally effective three point shot.
Whoever locks down the Celtics' starting spot at PF long term most likely isn't on the Celtics right now, and perhaps not even in the league.
Even this season, the best frontcourt combo for the Celts, given their other personnel, might end up being Amir and Zeller, or one of Amir and Zeller with Jerebko or Kelly. Versatility, mobility, and defense combined with reliable floor spacing and relatively low usage rates. These seem to be the qualities that Brad Stevens likes, and those qualities seem like they will mesh best with our current group of guards.