He's never been good defensively. People just assume he's a good defender because of his athleticism, but his lateral movement is pretty bad and his defense against pick and roll has always been atrocious.
I don't think so. This makes them slightly better, but what good does that do? Young can alao opt out after this season. Bennett just needs to be a role player, which I think is very possible, and Philly wins the trade big time.