Rivers was trying to find anybody who could play that pathetically horrible defensive concept that he was putting out there. The blitz is a gimmick...Rivers was too lazy to implement anything else.
Banks was a better individual defender than West. Blount was a better defender than Perk period at the time. But Garnett or Jordan wouldn't have been better defenders than Blount or West in that defense.
You realize that 1. the scheme was the same as it is now.
and 2. Doc had a defensive "guru" then, just like he does now.
The difference is that Tom Thibodeau is head and shoulders above Tony Brown, and they now have veteran players who are all buying in.
I really find it hard to blame Doc directly for the defense when they were terrible, but give him no credit now that it is good. Maybe you can blame him for giving Brown that kind of power (although I don't know if that was his or Ainge's call...or if anyone better would have come), but to blame Doc for the scheme, which is systematically the same as the one they are playing now, and succeeding with just doesn't work.