I think Avery can help.
The defense has been terrible. But why?
KG, Pierce, and Rondo are all back. As is Bass. Courtney Lee should actually be an upgrade over Ray at the 2. The starting lineup shouldn't be any worse defensively than it was last year at this time.
I think there are a few answers.
1) The team hasn't learned to play defense together, particularly the new players. This should get better over time.
2) The Sully/Bass 4/5 lineups offer no shotblocking. I'm all for playing one undersized PF (including Green), but playing 2 at a time at the 4/5 isn't helping.
3) Avery Bradley. While he may not solve all problem, he'll certainly help. For instance, he could've covered Holliday last night, who would've had a much more difficult night. And that could've been enough to eke out a win.