IMO, I think we should temper our high expectations of Sullinger next year. This is my take:  

1. Lets remember that he is he coming off serious back surgery and has just been cleared to play.  So conditioning will be an issue to start with.

2.  Part of Sully's success was using his wide body and physical play underneath. I would expect that he may be a bit more timid until gains confidence in his back strength.  He will be a different player and it will affect his productivity...for a while

3. Assuming he breaks into the lineup early, and I seriously doubt he starts or even gets 20 MPG in the first few months, he needs to reduce his fouls (better defensive footwork) to stay on the court.  Last year he averaged 3.5 fouls per game in less than 20 minutes.  Not good.  

4.  Sully is an undersized PF at 6'9" (really 6'8").  Forget about him playing Center position.  Not gonna happen.  He would be targeted, exploited and foul out in 15 minutes.  A proverbial lamb to slaughter.  Olynyk will play some center, not Sully.

5.  Realistically, at the PF position, both Bass and Humphries are more proven players with more experience.  Bass was the starter last year.  It is likely that he will be the starter this year.  As good as we thought Sully was last year and as bad as we think Hump was last year, his 13.67 was better than Sully's 13.52 PER.  Now add Oly to the competition and Sully minutes are reduced even more.

6. Last year, Sully had mentors, Pierce and especially in Garnett.  This year he is on his own and with very limited minutes last year, he still has a lot to learn about NBA play.  

Summary:  I believe that Sully is a key building block for our future. He is a proficient offensive rebounder with exceptional court sense.  It is likely IMO that Danny and Stevens bring Sully along very slowly for health and developmental reasons.  I do not expect Sully to get much playing time until January, where his minutes will increase and Bass and Humps minutes (if they are still on the team) decrease considerably.  Next year, Oly and Sully (two very different skill sets) share minutes at PF depending upon matchups and game situations...and Oly plays some center when we go small and fast.