Watching the highlight videos of Porzingis and Bender, it feels like Bender is really soft. Porzingis was always an aggressive rebounder even though he is a stick. I have a really bad feeling about Bender and the videos haven't really impressed me. One thing I also noted was that he is really bad around the rim from the highlights I saw on draft express. That's a big concern for a big guy.
Bottom line, Porzingis has makeup. I have no idea if that is the case with Bender. So if Ainge drafts him, he's probably going to be good since Ainge will get insight we don't have.