By simple math this had to be at least close to happening. His defensive +/- is close to half what it was earlier this year, the bench would need to be playing at his level or better for quite a while to shrink the number by that amount. People should be pretty familiar with this though, the bigs aside from KG improving their defense is a big part of the "Rondo effect".
There will probably be 3 possible responses to this on the board. Either try and blame Rondo, consider possible trade options for KG since his play on defense is holding the team back, or claim that it's crazy to draw such conclusions from those numbers (except for when Rondo's involved).
On second thought, the middle option above will never happen.