Here's the deal:
When you're drafting outside the lottery (as Danny generally has done since he's come here), you aren't going to get the prototypical player who has all the skills you'd like for his position. You're either going to get an athlete with size that you hope you can turn into a player or a player who has some sort of flaw (size, as with BBD, Powe, Gomes) or attitude(Rondo, TA), or in some cases a mixture of both or more things.
The history of turning athletes with size into players is not very good in the NBA, particularly in Boston. Look at the likes of Jerome Moiso, Kedrick Brown, Marcus Banks, and J.R. Giddens. All were great athletes with prototypical size. None could actually play.
In fact, I think some of Danny's biggest hits have been going with guys who can play, but weren't actually the right size (like BBD, Powe, Gomes, TA, and Bradley).
So is Sullinger a guarantee to be the next David West or Carlos Boozer? No. But drafting a guy who knows how to play the game, but is an inch or two shorter is a better idea that drafting some 7-0 athletic guy who will never amount to more than a Jerome Moiso or a Ryan Hollins (though I like Hollins, but he's certainly not a building block for a franchise).