George Karl's defenses calls for an option of gambling in the passing lanes, and switches.
There's no problem with this...except, when you have someone like Belinelli on a Klay Thompson, or Rondo on a Andre Drummond.
I specifically singled out Belinelli because he's a poor defender. He has troubles getting through screens and catching up with his man. Unlike Ben, when Belinelli tries to go for the steal in the lane, he can't recover in time. This leads to too many open shots. The guys need better awareness. On deadly shooters, you should not leave them. On guys who aren't strong shooters, it's ok to leave them.
Rondo always switches really early for some reason. I don't think switching is all that bad, but there's a time and place for it. At the end of close games is not the time for it.
A lot of this team's defensive problems is on the lack of how to do it, like you said. We don't have the personnel to become a good defensive team. Rondo is an inconsistent defender, and with him, I think it's the effort part. Ben might be our best perimeter defender. Gay has been below average, to average. WCS is not great on boards, and has a tendency to over-help sometimes. Cousins is an average defender.
There is no real + defender like many of these other teams have. I hope that's what Ben can be.