I will humbly submit that KO's middling rebounding has little to do with the Celts' being "saturated" with other rebounders.
Could be, but our best rebounder, can't get in shape, is slow and will be even in shape and can't spread the floor. Mickey is the closest thing we have in the pipeline as a complete big. Amir and Jonas are but they are hardly stars but they are competent. Most of our bigs have flaws though.
David Lee is hopefully in shape this season.
And most players have flaws. Like, virtually all. Maybe LeBron 2012-2013 was flawless (aside from being LeBron), but it's pretty rare. Olynyk's flaw is that he gets exploited defensively and on the boards. He's also a fine shooter, especially for a big, but he's not elite at it. His passing is probably a bit overrated, with a near 1:1 assist-turnover ratio.
Turner is a very inconsistent shooter. But he's also capable of running an offense from the 3, and rebounds great for his position.
Porter has been so far limited offensively. He's a good defender at multiple positions. His offense might come around, making him a much more complete player. He's young still, so has the most room to grow. He's probably not a superstar in the making, but probably does havethe ceiling as #3 guy on a great team, which is higher than Olynyk or Turner. At the same time, maybe he turns into another Jeff Green, or never even gets that far.
Playing next to Gortat would help cover some of Olynyk's weakness, both in defense and rebounding, while having playmakers like Wall and Beal around him could emphasize his strengths. On the other hand, more would be asked of Porter in Boston, giving him the opportunity to expand his game and reach his full potential.