Olynyk is a 'tweener player. He's a perimeter player in a 7 foot body. He can pass and shoot outside. That's about it, as far as I can tell. He isn't great around the basket because he can't get off his feet. I watched him one game for 10 minutes, and he never got off his feet! Even around the basket. Those defense numbers I see quoted once in a while about him are an illusion. So much for quantifying defense. For big guys, it's rebounding and blocked shots.
I don't know what Ainge sees in this guy, other than being a 7 foot 3P shooter. He and Zeller are both weak defenders against other inside bigs around the league. Horford and Johnson are plus bigs, at least when Johnson shows up to play, but Sullinger was a better rebounder than KO and Zeller. Rebounding is their weakness, and they will miss him. I'm disappointed Ainge didn't draft a big who can jump, though Brown doesn't look like a bad pick. At least he can jump.