There's an old saying, "You can't make chicken salad out of chicken shit."
While you can work on team defense fundamentals and reach a certain level of competence, at the end of the day, if the players on the court are physically limited. you're simply not going to get great results. The best you can do is work on effort, hustle and determination, and hope.
That said, my biggest concern with this team remains its lack of leadership and cohesiveness. I was at the ND-Virginia Tech game last night, and was reminded of how good teams almost always have several core players that work at building that camaraderie. Our players basically just stand around in their own little worlds in dead ball situations or immediately after a play. Good teams have players that are clapping, fist bumping, encouraging each other, smiling, etc. IMO, that is by far the biggest issue with this squad.